Display device and operation method thereof

ABSTRACT

To provide a display device having an input means using a bending action. A display device includes a first substrate, a second substrate, a display part, a first sensor element, and a second sensor element. The display part is provided between the first substrate and the second substrate. The first sensor element and the second sensor element are provided in their respective regions overlapping with the display part between the first substrate and the second substrate. The region where the second sensor element is provided overlaps with the region where the first sensor element is provided. The first substrate and the second substrate have flexibility. The first sensor element has a function of detecting the presence or absence of an object touching the first substrate or the second substrate. The second sensor element has a function of detecting the distortion of the first substrate or the second substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 14/700,663, filed Apr. 30, 2015, now allowed, which claims the benefit of a foreign priority application filed in Japan as Serial No. 2014-095200 on May 2, 2014, both of which are incorporated by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

One embodiment of the present invention relates to a semiconductor device and a display device including the semiconductor device.

Note that one embodiment of the present invention is not limited to the above technical field. The technical field of one embodiment of the invention disclosed in this specification and the like relates to an object, a method, or a manufacturing method. In addition, one embodiment of the present invention relates to a process, a machine, manufacture, a program, or a composition of matter. Specifically, examples of the technical field of one embodiment of the present invention disclosed in this specification include a semiconductor device, a display device, a liquid crystal display device, a light-emitting device, a lighting device, a power storage device, a storage device, a method for driving any of them, and a method for manufacturing any of them.

In this specification and the like, a semiconductor device generally means a device that can function by utilizing semiconductor characteristics. A transistor and a semiconductor circuit are embodiments of semiconductor devices. In some cases, a storage device, a display device, or an electronic device includes a semiconductor device.

2. Description of the Related Art

In recent years, display devices have been applied to a variety of uses and essential to portable electronic appliances and the like. Display devices used for portable electronic appliances and the like are required to be thin and lightweight and to have a narrow bezel, for example. Furthermore, display devices to which flexibility is imparted are expected to be applied to other uses.

For example, Patent Document 1 discloses, as a flexible display device, an active matrix light-emitting device in which an organic EL element and a transistor serving as a switching element are provided over a film substrate.

REFERENCE Patent Document

-   [Patent Document 1] Japanese Published Patent Application No.     2003-174153

SUMMARY OF THE INVENTION

Application of a flexible display device utilizing its flexibility as in a curved display or the like is expected. Furthermore, an action such as bending can be used as an input means.

An object of one embodiment of the present invention is to provide a flexible display device. Another object is to provide a display device having an input means using a bending action. Another object is to provide a lightweight display device. Another object is to provide a thin display device. Another object is to provide a display device including a distortion sensor. Another object is to provide a display device including a touch sensor. Another object is to provide a novel display device or the like. Another object is to provide an operation method of the display device. Another object is to provide a program for operating the display device. Another object is to provide a novel semiconductor device or the like. Another object is to provide an operation method of the semiconductor device or the like. Another object is to provide a program for operating the semiconductor device or the like.

Note that the descriptions of these objects do not disturb the existence of other objects. In one embodiment of the present invention, there is no need to achieve all the objects. Other objects will be apparent from and can be derived from the description of the specification, the drawings, the claims, and the like.

One embodiment of the present invention relates to a display device having an input means using the action of bending the display device.

One embodiment of the present invention is a display device including a first substrate, a second substrate, a first element layer, and a second element layer. The first substrate and the second substrate have flexibility. The first element layer is provided between the first substrate and the second substrate. The second element layer is provided between the first substrate and the second substrate. The first element layer and the second element layer overlap with each other. The first element layer includes a display part and a first sensor element part. A top surface shape of the display part is substantially rectangular. The first sensor element part overlaps with the display part. The second element layer includes second sensor element parts. The second sensor element parts overlap with a first region along a first side of the display part, a second region along a second side facing the first side, and a third region intermediate between the first side and the second side. The first sensor element part is configured to detect presence or absence of an object touching the first substrate or the second substrate. The second sensor element parts are configured to detect distortion of the first substrate or the second substrate.

In this specification, ordinal numbers such as “first”, “second”, and the like are used in order to avoid confusion among components, and the terms do not limit the components numerically.

Another embodiment of the present invention is a display device including a first substrate, a second substrate, a third substrate, a fourth substrate, a first element layer, and a second element layer. The first substrate and the second substrate have flexibility. The third substrate is provided between the first substrate and the second substrate. The fourth substrate is provided between the first substrate and the second substrate. The third substrate and the fourth substrate are provided next to each other in positions not overlapping with each other. The first element layer is provided between the first substrate and the second substrate. The first element layer has a region overlapping with the third substrate. The first element layer has a region overlapping with the fourth substrate. The second element layer is provided between the first substrate and the second substrate. The second element layer has a region overlapping with the third substrate. The second element layer has a region overlapping with the fourth substrate. The first element layer and the second element layer overlap with each other. The first element layer includes a display part and a first sensor element part. A top surface shape of the display part is substantially rectangular. The first sensor element part overlaps with the display part. The second element layer includes second sensor element parts. The second sensor element parts overlap with a first region along a first side of the display part, a second region along a second side facing the first side, and a third region intermediate between the first side and the second side. The second sensor element parts overlap with the third substrate and/or the fourth substrate. The first sensor element part is configured to detect presence or absence of an object touching the first substrate or the second substrate. The second sensor element parts are configured to detect distortion of the first substrate or the second substrate.

The display part is capable of being bent along a region between the third substrate and the fourth substrate when seen from a display surface.

It is preferable that the third substrate be more rigid than the first substrate and the second substrate and the fourth substrate be more rigid than the first substrate and the second substrate.

The third substrate and the fourth substrate have flexibility.

An insulating layer may be provided between the first element layer and the second element layer.

The first sensor element can be a metal thin film resistor.

The display part can include an organic EL element.

Another embodiment of the present invention is a method for operating a display device, including: a first step of displaying a first image on a display part; a second step of determining whether a curvature of an edge or a vicinity of a center of the display part is larger than or equal to a first set value; a third step of displaying an image for operation on the edge of the display part; a fourth step of detecting, on the image for operation, a position of an object touching the image; a fifth step of detecting, on the image for operation, a position of the object touching the image; a sixth step of determining whether a curvature of the edge of the display part is larger than or equal to a second set value; and a seventh step of changing the first image to a second image. When the curvature is smaller than the first set value in the second step, the determination of the curvature is performed again. When the curvature is larger than or equal to the first set value in the second step, a process proceeds to the third step. When a change in the position of the object is not detected in the fifth step, the process proceeds to the sixth step. When a change in the position of the object is detected in the fifth step, the process proceeds to the seventh step. When the curvature is smaller than the second set value in the sixth step, the process returns to the fifth step. When the curvature is larger than or equal to the second set value in the sixth step, the process proceeds to the seventh step.

The process from the first step to the seventh step may be performed sequentially and repeatedly while the image displayed on the display part in the seventh step is used as the image displayed on the display part in the first step.

With one embodiment of the present invention, a flexible display device can be provided, a display device having an input means using a bending action can be provided, a lightweight display device can be provided, a thin display device can be provided, a display device including a distortion sensor can be provided, a display device including a touch sensor can be provided, a novel display device or the like can be provided, an operation method of the display device can be provided, a program for operating the display device can be provided, a novel semiconductor device or the like can be provided, an operation method of the semiconductor device or the like can be provided, or a program for operating the semiconductor device or the like can be provided

Note that the description of these effects does not disturb the existence of other effects. One embodiment of the present invention does not necessarily achieve all the effects listed above. Other effects will be apparent from and can be derived from the description of the specification, the drawings, the claims, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are a top view and a cross-sectional view illustrating a display device.

FIGS. 2A to 2C are cross-sectional views each illustrating a display device.

FIGS. 3A and 3B are a top view and a cross-sectional view illustrating a display device.

FIGS. 4A to 4F are top views illustrating the positions of regions where distortion sensor elements are provided.

FIG. 5 is a top view illustrating a display device.

FIGS. 6A and 6B are a cross-sectional view illustrating a display device and a top view of a distortion sensor element.

FIG. 7 is a cross-sectional view illustrating a display device.

FIG. 8 is a block diagram illustrating a display device.

FIGS. 9A and 9B illustrate modes of a display device.

FIGS. 10A to 10C illustrate modes of a display device.

FIGS. 11A and 11B illustrate operations of a display device.

FIGS. 12A and 12B illustrate operations of a display device.

FIGS. 13A and 13B illustrate operations of a display device.

FIGS. 14A and 14B each illustrate a distortion sensor circuit.

FIG. 15 illustrates a distortion sensor circuit and a pixel circuit.

FIG. 16 illustrates a distortion sensor circuit and a pixel circuit.

FIG. 17 illustrates a distortion sensor circuit and a pixel circuit.

FIG. 18 illustrates a distortion sensor circuit and a pixel circuit.

FIG. 19 illustrates a read circuit.

FIG. 20 illustrates a distortion sensor circuit and a pixel circuit.

FIG. 21 illustrates a distortion sensor circuit and a pixel circuit.

FIGS. 22A and 22B are each a cross-sectional view illustrating a transistor.

FIGS. 23A and 23B are each a cross-sectional view illustrating a transistor.

FIGS. 24A and 24B are each a cross-sectional view illustrating a transistor.

FIGS. 25A and 25B are each a cross-sectional view illustrating a transistor.

FIGS. 26A and 26B are each a cross-sectional view illustrating a transistor.

FIGS. 27A and 27B are each a cross-sectional view illustrating a transistor.

FIGS. 28A and 28B are each a cross-sectional view illustrating a transistor.

FIGS. 29A and 29B are each a cross-sectional view illustrating a transistor.

FIGS. 30A and 30B are each a top view illustrating a transistor.

FIG. 31 is a perspective view illustrating a display module.

FIGS. 32A and 32B illustrate an example of a touch panel.

FIGS. 33A, 33B1, 33B2, and 33C illustrate examples of configurations and driving methods of a sensing circuit and a converter.

FIGS. 34A to 34C illustrate an example of a sensing circuit.

FIG. 35 is a cross-sectional view illustrating a touch panel.

FIGS. 36A and 36B illustrate an electronic appliance.

FIG. 37 is a flow chart of operation of a display device.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments will be described in detail with reference to drawings. Note that the present invention is not limited to the following description and it will be readily appreciated by those skilled in the art that modes and details can be modified in various ways without departing from the spirit and the scope of the present invention. Therefore, the present invention should not be interpreted as being limited to the description of embodiments below. Note that in structures of the present invention described below, the same portions or portions having similar functions are denoted by the same reference numerals in different drawings, and description thereof is not repeated in some cases. It is also to be noted that the same components are denoted by different hatching patterns in different drawings, or the hatching patterns are omitted in some cases.

Note that in this specification and the like, when it is explicitly described that X and Y are connected, the case where X and Y are electrically connected, the case where X and Y are functionally connected, and the case where X and Y are directly connected are included therein. Here, X and Y each denote an object (e.g., a device, an element, a circuit, a wiring, an electrode, a terminal, a conductive film, or a layer). Accordingly, a connection relationship other than those shown in drawings and texts is also included without limitation to a predetermined connection relationship, for example, the connection relationship shown in the drawings and the texts.

For example, in the case where X and Y are electrically connected, one or more elements that enable electrical connection between X and Y (e.g., a switch, a transistor, a capacitor, an inductor, a resistor, a diode, a display element, a light-emitting element, or a load) can be connected between X and Y. A switch is controlled to be on or off That is, a switch is turned on or off (is brought into an on state or an off state) to determine whether current flows therethrough or not. Alternatively, the switch has a function of selecting and changing a current path.

For example, in the case where X and Y are functionally connected, one or more circuits that enable functional connection between X and Y (e.g., a logic circuit such as an inverter, a NAND circuit, or a NOR circuit; a signal converter circuit such as a DA converter circuit, an AD converter circuit, or a gamma correction circuit; a potential level converter circuit such as a power supply circuit (e.g., a step-up circuit or a step-down circuit) or a level shifter circuit for changing the potential level of a signal; a voltage source; a current source; a switching circuit; an amplifier circuit such as a circuit that can increase signal amplitude, the amount of current, or the like, an operational amplifier, a differential amplifier circuit, a source follower circuit, or a buffer circuit; a signal generation circuit; a memory circuit; and/or a control circuit) can be connected between X and Y. Note that for example, in the case where a signal outputted from X is transmitted to Y even when another circuit is interposed between X and Y, X and Y are functionally connected.

Note that when it is explicitly described that X and Y are connected, the case where X and Y are electrically connected (i.e., the case where X and Y are connected with another element or another circuit positioned therebetween), the case where X and Y are functionally connected (i.e., the case where X and Y are functionally connected with another element or another circuit positioned therebetween), and the case where X and Y are directly connected (i.e., the case where X and Y are connected without another element or another circuit positioned therebetween) are included therein. That is, when it is explicitly described that “X and Y are electrically connected”, the description is the same as the case where it is explicitly only described that “X and Y are connected”.

Even when independent components are electrically connected to each other in a circuit diagram, one component has functions of a plurality of components in some cases. For example, when part of a wiring also functions as an electrode, one conductive film functions as the wiring and the electrode. Thus, “electrical connection” in this specification includes in its category such a case where one conductive film has functions of a plurality of components.

Note that for example, the case where a source (or a first terminal or the like) of a transistor is electrically connected to X through (or not through) Z1 and a drain (or a second terminal or the like) of the transistor is electrically connected to Y through (or not through) Z2, or the case where a source (or a first terminal or the like) of a transistor is directly connected to one part of Z1 and another part of Z1 is directly connected to X while a drain (or a second terminal or the like) of the transistor is directly connected to one part of Z2 and another part of Z2 is directly connected to Y, can be expressed by using any of the following expressions. The expressions include, for example, “X, Y, a source (or a first terminal or the like) of a transistor, and a drain (or a second terminal or the like) of the transistor are electrically connected to each other, and X, the source (or the first terminal or the like) of the transistor, the drain (or the second terminal or the like) of the transistor, and Y are electrically connected to each other in this order”, “a source (or a first terminal or the like) of a transistor is electrically connected to X, a drain (or a second terminal or the like) of the transistor is electrically connected to Y, and X, the source (or the first terminal or the like) of the transistor, the drain (or the second terminal or the like) of the transistor, and Y are electrically connected to each other in this order”, and “X is electrically connected to Y through a source (or a first terminal or the like) and a drain (or a second terminal or the like) of a transistor, and X, the source (or the first terminal or the like) of the transistor, the drain (or the second terminal or the like) of the transistor, and Y are provided to be connected in this order”. When the connection order in a circuit configuration is defined by an expression similar to the above examples, a source (or a first terminal or the like) and a drain (or a second terminal or the like) of a transistor can be distinguished from each other to specify the technical scope. Note that these expressions are examples and there is no limitation on the expressions. Here, X, Y, Z1, and Z2 each denote an object (e.g., a device, an element, a circuit, a wiring, an electrode, a terminal, a conductive film, or a layer).

Note that the terms “film” and “layer” can be interchanged with each other depending on the case or circumstances. For example, the term “conductive layer” can be changed into the term “conductive film” in some cases. In addition, the term “insulating film” can be changed into the term “insulating layer” in some cases.

Embodiment 1

In this embodiment, a display device of one embodiment of the present invention will be described with reference to drawings.

The “display device” in this specification means an image display device or a light source (including a lighting device). Further, the display device includes any of the following modules in its category: a module including a connector such as a flexible printed circuit (FPC), or tape carrier package (TCP); a module including TCP which is provided with a printed wiring board at the end thereof; and a module including a driver circuit which is directly mounted on a display element by a chip on glass (COG) method.

The display device that is one embodiment of the present invention has flexibility (flexible display device). Note that “flexible device” means that a device can be bent or warped.

FIG. 1A is a schematic top view illustrating a display device of one embodiment of the present invention. FIG. 1B is a cross-sectional view of FIG. 1A. The display device includes a substrate 41, a substrate 42, a substrate 43, a substrate 44, a substrate 48, an element layer 51, and an element layer 52. Note that the substrate 42 is not shown in FIG. 1A.

The element layer 51 is provided in contact with one surface of the substrate 48, and the substrate 42 is provided in contact with the element layer 51. The element layer 52 is provided in contact with the other surface of the substrate 48, and the substrate 43 and the substrate 44 are provided in contact with the element layer 52. Here, the substrate 43 and the substrate 44 are provided with a space therebetween so as not to overlap with each other. The substrate 41 is provided in contact with the element layer 52, the substrate 43, and the substrate 44.

The substrate 41, the substrate 42, and the substrate 48 have flexibility. It is preferable that the substrate 41, the substrate 42, and the substrate 48 be formed using the same material and have the same thickness to prevent a warp due to thermal expansion or the like. Note that the substrate 41, 42, or 48 and the layer or the substrate in contact therewith can be bonded to each other using a bonding layer or the like not shown.

Note that the substrate 48 may be an insulating layer formed of silicon oxide, aluminum oxide, or the like. As shown in FIG. 2A, the substrate 48 is not necessarily provided.

The substrate 43 and the substrate 44 are preferably more rigid than the substrate 41, the substrate 42, and the substrate 48. In the display device having such a structure, a specific region can be bent easily. In the structure shown in FIGS. 1A and 1B, a region between the substrate 43 and the substrate 44 can be bent easily. In addition, a region outer than a side of the substrate 43 which is substantially parallel to facing sides of the substrate 43 and the substrate 44 and is farther from the substrate 44 in the top view can be bent easily. Furthermore, a region outer than a side of the substrate 44 which is substantially parallel to facing sides of the substrate 43 and the substrate 44 and is farther from the substrate 43 in the top view can be bent easily.

The rigidity of the substrate 43 and the substrate 44 may be the same as that of the substrate 41, the substrate 42, and the substrate 48. In this structure, the mechanical strength of a region including the substrate 43 and the substrate 44 is increased owing to the thicknesses of the substrate 43 and the substrate 44. Therefore, in a manner similar to that described above, a specific region can be bent easily. In the case where the thickness of the substrate 41 is partly increased, the substrate 43 and the substrate 44 may be omitted.

Note that the material, the thickness, and the like of each of the substrates may be selected as appropriate so that given regions can have the same degree of flexibility. In this case, the substrate 43 and the substrate 44 may be omitted as shown in FIGS. 3A and 3B.

The element layer 51 includes a display part 47 and a touch sensor 49. As a display element provided in the display part 47, typically, an organic EL element can be used. Instead of an organic EL element, an inorganic EL element can be used. Alternatively, a liquid crystal element can be used. For example, a reflective display device can be provided by combination of a liquid crystal element and a reflective electrode. A transmissive display device can be provided by combination of a liquid crystal element and a thin light source such as an organic EL element. A semi-transmissive display device can be provided by combination of a liquid crystal element, a reflective electrode, and a thin light source.

As the touch sensor 49, a capacitive-type touch sensor, an optical-type touch sensor, a pressure-sensitive type touch sensor, or the like can be used. Note that the position of the touch sensor 49 is not limited to that overlapping with the display part 47 as shown in the drawing. The touch sensor 49 may be incorporated in the display part. Alternatively, the touch sensor 49 may be provided between the substrate 42 and the element layer 51. Still alternatively, the touch sensor 49 may be provided over the substrate 42.

The element layer 51 includes a first circuit electrically connected to the display element. The first circuit can have a function as a pixel circuit. When the display element is an organic EL element, a circuit configuration including two transistors and one capacitor can be employed, for example. When the display element is a liquid crystal element, a circuit configuration including one transistor and one capacitor can be employed.

The element layer 52 includes a sensor capable of indirectly sensing distortion of the substrate 41 and/or the substrate 42. Specifically, a distortion sensor element can be used as the sensor. As the distortion sensor element, typically, a metal thin film resistor can be used. The amount of distortion in the vicinity of the region where the metal thin film resistor is provided can be measured on the basis of the amount of change in the resistance of the metal thin film resistor. As the distortion sensor element, a piezoelectric element can also be used. As the piezoelectric element, an element including a piezoelectric substance such as barium titanate, lead zirconate titanate, or zinc oxide can be used.

The distortion sensor element is provided in a region 46 shown in FIGS. 1A and 1B, for example. Note that the number of distortion sensor elements to be provided in the region 46 is not limited to one, and a plurality of distortion sensor elements may be provided in the region 46. Although the region 46 partly overlaps with the substrate 43 and/or the substrate 44 in FIGS. 1A and 1B, a structure in which the region 46 overlaps with neither the substrate 43 nor the substrate 44 can be employed, or a structure in which the region 46 wholly overlaps with the substrate 43 and/or the substrate 44 can be employed.

The element layer 52 can include a second circuit electrically connected to the distortion sensor element. The second circuit has a function of reading the amount of change in the resistance of the distortion sensor element. The second circuit can include, for example, two or three transistors and a resistor. Note that the second circuit is not necessarily included in the element layer 52 and may be attached externally.

Alternatively, as shown in FIG. 2B, the display part 47 and the region 46 including the distortion sensor element may be provided in the element layer 51. In this case, the element layer 51 can include the first circuit electrically connected to the display element and the second circuit electrically connected to the distortion sensor element. Note that the second circuit may be attached externally.

Still alternatively, as shown in FIG. 2C, a substrate 45 may be provided between the element layer 52 and the substrate 43, the substrate 44, and the substrate 41. Note that the substrate 45 may be an insulating layer.

The orientation of the distortion sensor element provided in the region 46 is set so that the distortion sensor element can detect a bend in a direction indicated by an arrow in the region 46 shown in FIG. 1A. For example, in the case where the top surface of the display part 47 is substantially rectangular as shown in the drawing, the distortion sensor elements are provided in a region along a first side of the display part 47, a region along a second side facing the first side, and a region intermediate between the first side and the second side. Thus, the action of bending the display device in half along its center and the action of bending an edge of the display device can be sensed.

Linking the bending action to a display function enables the display device to be operated by an action similar to that of reading a book. Specifically, operation such as displaying an image, turning off the display, or changing the image can be performed by the action of opening or closing a book, turning a page, or the like given to the display device.

Note that the region 46 where the distortion sensor element is provided is not limited to the positions in the examples shown in FIG. 1A and FIG. 3A, and may be provided in positions shown in FIGS. 4A to 4F. Even when the region 46 is provided in the positions shown in FIGS. 4A to 4F, the above-described bending action can be detected. Note that the number of and the distance between the regions 46 shown in FIG. 1A, FIG. 3A, and FIGS. 4A to 4F are examples and not limited to those shown in the drawings.

FIG. 5 shows an example of a top view of the display part 47, the distortion sensor element included in the region 46, and driver circuits.

In the display part 47, pixels 81 are arranged in a matrix and each include the display element and the first circuit. The first circuit is electrically connected to a circuit 71 and a circuit 72. The circuit 71 can function as a signal line driver circuit (source driver), for example. The circuit 72 can function as a scan line driver circuit (gate driver), for example.

A distortion sensor element 82 can be provided in part of the pixels 81 or provided to overlap with part of the pixels 81.

The second circuit can be included in the pixel 81. Alternatively, the second circuit can be provided to overlap with the pixel 81. Still alternatively, the second circuit can be attached externally. A circuit 73 and a circuit 74 are a circuit selecting the distortion sensor element 82 and a circuit for reading a signal, respectively. The second circuit can also be included in any of the circuit 73 and the circuit 74.

FIG. 6A is an example of a cross-sectional view of part of a display device that includes an organic EL element as a display element. Note that FIG. 6A illustrates part of typical structures in a region 302 including the display element in the pixel 81 and the distortion sensor element 82 shown in FIG. 5, a region 306 including a driver circuit, and a flexible printed circuit (FPC) connection region 305. FIG. 6B is a top view of the distortion sensor element 82, and FIG. 6A illustrates a cross section along the dotted line in FIG. 6B. The distortion sensor element 82 can detect a change in shape in the direction indicated by the arrow. Note that detailed description of the touch sensor 49 is omitted.

The region 306 can include the second circuit, the circuit 71, the circuit 72, the circuit 73, the circuit 74, or the like. Note that part or all of the second circuit, the circuit 71, the circuit 72, the circuit 73, and the circuit 74 may be an external IC chip or external IC chips.

The display device illustrated in FIG. 6A, which is an example of the display device illustrated in FIG. 1A, has a region in which the substrate 41, the substrate 43, the element layer 52, the substrate 48, an insulating film 321 a, the element layer 51, an insulating film 321 b, and the substrate 42 are stacked in this order. Note that the substrate 41, the substrate 42, the substrate 43, or the substrate 48 and the layer or the substrate in contact therewith may be provided with a bonding layer or the like (not shown) therebetween.

As the insulating film 321 a and the insulating film 321 b, a single layer of a silicon oxide film, a silicon oxynitride film, a silicon nitride film, or a silicon nitride oxide film, or a stacked layer including any of the films can be used.

In FIG. 6A, the element layer 51 includes a transistor 350, a transistor 354 a, a transistor 354 b, an insulating film 364, an insulating film 368, a planarization insulating film 370, a connection electrode 360, a conductive film 372, a conductive film 374, an insulating film 334, a sealing layer 432, a coloring layer (color filter) 336, and a light-blocking layer (black matrix) 338. The element layer 51 is hermetically sealed with the substrate 41, the substrate 48, the sealing layer 432, and a sealing material 312. Note that there is a case where part of the above components is not included or a component other than the above components is included in the element layer 51.

The element layer 52 includes the distortion sensor element 82 and a planarization insulating film 371. Note that the second circuit for reading a change in the resistance of the distortion sensor element 82 may be provided in the element layer 52.

The insulating film 364 can be formed using, for example, silicon oxide or silicon oxynitride. The insulating film 364 is preferably formed using an oxide insulating film containing oxygen in excess of that in the stoichiometric composition. The insulating film 368 has a function of blocking oxygen, hydrogen, water, an alkali metal, an alkaline earth metal, or the like. For example, a nitride insulating film is preferably used.

The planarization insulating films 370 and 371 can be formed using a heat-resistant organic material, such as a polyimide resin, an acrylic resin, a polyimide amide resin, a benzocyclobutene resin, a polyamide resin, or an epoxy resin. Note that the planarization insulating films 370 and 371 may be formed by stacking a plurality of insulating films formed from these materials.

In the region 302, the transistor 350 is included in the first circuit and is electrically connected to an organic EL element 480. The organic EL element 480 includes the conductive film 372, an EL layer 446, and the conductive film 374. The display device illustrated in FIG. 6A is capable of displaying an image by light emission from the EL layer 446 included in the organic EL element 480.

An insulating film 430 is provided over the conductive film 372 over the planarization insulating film 370. The insulating film 430 covers part of the conductive film 372. A conductive film with high properties of reflecting light emitted from the EL layer 446 is used for the conductive film 372, and a conductive film with high properties of transmitting the light is used for the conductive film 374, whereby the organic EL element 480 can have a top emission structure. Alternatively, a conductive film with high properties of transmitting the light is used for the conductive film 372, and a conductive film with high properties of reflecting the light is used for the conductive film 374, whereby the organic EL element 480 can have a bottom emission structure. Further alternatively, a conductive film with high properties of transmitting the light is used for both the conductive film 372 and the conductive film 374, whereby a dual emission structure can be obtained.

For the insulating film 430, an organic resin or an inorganic insulating material can be used, for example. As the organic resin, for example, a polyimide resin, a polyamide resin, an acrylic resin, a siloxane resin, an epoxy resin, a phenol resin, or the like can be used. As the inorganic insulating material, silicon oxide, silicon oxynitride, or the like can be used, for example.

The coloring layer 336 is provided to overlap with the organic EL element 480, and the light-blocking layer 338 is provided to overlap with the insulating film 430. The coloring layer 336 and the light-blocking layer 338 are covered with the insulating film 334. A space between the organic EL element 480 and the insulating film 334 is filled with the sealing layer 432.

For the sealing layer 432, a solid sealing material with flexibility can be used. For example, a glass material such as a glass frit, or a resin material such as a two-component-mixture-type resin which is curable at room temperature, a light curable resin, a thermosetting resin, and the like can be used.

Although a structure with the coloring layer 336 is described as the display device in FIG. 6A, the structure is not limited thereto. In the case where the EL layers 446 with different emission colors are selectively formed, the coloring layer 336 is not necessarily provided. The color of the coloring layer 336 is not limited to three colors of R (red), G (green), and B (blue). For example, a display unit may be composed of four pixels of the R pixel, the G pixel, the B pixel, and a W (white) pixel. Alternatively, a color element may be composed of two colors among R, G, and B as in PenTile layout. The two colors may differ among display units. Alternatively, one or more colors of yellow, cyan, magenta, and the like may be added to RGB. Further, the size of a display region may be different depending on respective dots of the color components. Embodiments of the disclosed invention are not limited to a display device for color display; the disclosed invention can also be applied to a display device for monochrome display.

Each of the substrate 41, the substrate 42, the substrate 43, the substrate 44, and the substrate 48 is preferably formed using a material with high toughness. Thus, a light-emitting device with high impact resistance that is less likely to be broken can be provided. For example, when an organic resin substrate is used as the substrate 41 and the substrate 42, the display device can be lightweight and unlikely to broken as compared to the case where a glass substrate is used as the substrate.

For the substrate 41, the substrate 42, the substrate 43, the substrate 44, and the substrate 48, for example, a material selected from the following can be used: glass which is thin enough to have flexibility, polyester resins such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), a polyacrylonitrile resin, a polyimide resin, a polymethyl methacrylate resin, a polycarbonate (PC) resin, a polyethersulfone (PES) resin, a polyamide resin, a cycloolefin resin, a polystyrene resin, a polyamide imide resin, a polyvinyl chloride resin, and a polyether etherketone (PEEK) resin. In particular, a material whose thermal expansion coefficient is low is preferred, and for example, a polyamide imide resin, a polyimide resin, or PET is preferably used. A substrate in which a glass fiber is impregnated with an organic resin or a substrate whose thermal expansion coefficient is reduced by mixing an organic resin with an inorganic filler can also be used.

The FPC connection region 305 includes the connection electrode 360, an anisotropic conductive film 380, and an FPC 316. The connection electrode 360 can be formed in a step of forming the source electrode layer and the drain electrode layer of the transistor. The connection electrode 360 is electrically connected to a terminal included in the FPC 316 through the anisotropic conductive film 380.

Note that the distortion sensor element 82 senses change in resistance due to expansion and contraction of the metal thin film; thus, one surface and the other surface of the metal thin film are preferably in contact with different materials having the respective mechanical properties (e.g., elastic modulus, bending strength, a Young's modulus, Poisson's ratio, or hardness) so that the metal thin film can easily expand and contract. For example, in the structure in FIG. 6A, one surface is in contact with the planarization insulating film 371, and the other surface is in contact with the substrate 41. Here, since the planarization insulating film 371 and the substrate 41 are formed using materials with different mechanical properties, the surface on which the metal thin film can expand and contract relatively easily is determined. Therefore, for example, the metal thin film expands when the shape is changed to be convex, and the metal thin film contracts when the shape is changed to be concave. Accordingly, the direction of change in shape can be sensed on the basis of the resistance when the metal thin film expands and the resistance when the metal thin film contracts.

The display device of one embodiment of the present invention may have a structure illustrated in a cross-sectional view in FIG. 7. A display device shown in FIG. 7 is an example of the display device shown in FIG. 2B. Note that description of a portion common to the display device shown in FIGS. 6A and 6B is omitted.

FIG. 7 illustrates part of typical structures in the region 302 including the display element in the pixel 81 and the distortion sensor element 82 shown in FIG. 5, the region 306 including the driver circuit, and the flexible printed circuit (FPC) connection region 305.

In the region 306, the transistor 352 can be included in the second circuit. In this case, electrodes of the distortion sensor element 82 are electrically connected to the respective wirings. One of the wirings is electrically connected to a gate electrode of the transistor 352.

In the region 306, a transistor 354 can be included in the circuit 71, the circuit 72, the circuit 73, or the circuit 74.

In the structures of the display devices illustrated in FIG. 6A and FIG. 7, two or more distortion sensor elements may be provided at different heights (in the thickness direction) between the substrate 41 and the substrate 42. The distortion sensor element may be provided over the substrate 41, the substrate 42, or both the substrate 41 and the substrate 42.

The transistor in the above display device is preferably a transistor whose channel formation region is formed in an oxide semiconductor layer.

Since the transistor using an oxide semiconductor layer has high mobility, an area occupied by transistors can be made small, and the aperture ratio can be increased. With use of the transistor, the circuits 71 to 74 can be formed over the substrate provided with the pixel 81. In addition, the transistor has extremely low off-state current and can hold a video signal or the like for a longer period; thus, the frame frequency can be lowered, and the power consumption of the display device can be reduced.

Furthermore, a transistor including an oxide semiconductor layer is preferably used as the transistor electrically connected to the distortion sensor element 82. By the use of a transistor with an extremely low off-state current as the transistor, electric charge which is unnecessarily input and output into and from an output wiring or the like can be inhibited.

The oxide semiconductor layer preferably includes a c-axis aligned crystal. In the case where the oxide semiconductor layer including the crystal is used for a channel formation region of the transistor, a crack or the like is less likely to occur in the oxide semiconductor layer when the display device is bent, for example. As a result, the reliability can be improved.

Note that the transistor including an oxide semiconductor layer is merely an example, and a transistor including an amorphous silicon layer or a polycrystalline silicon layer can also be used. Alternatively, a transistor including an organic semiconductor may be used. Examples of an organic semiconductor include acenes such as tetracene and pentacene, oligothiophene derivatives, phthalocyanines, perylene derivatives, rubrene, Alq₃, TTF-TCNQ, polythiophene (e.g., poly(3-hexylthiophene) (P3HT)), polyacetylene, polyfluorene, polyphenylene vinylene, polypyrrole, polyaniline, anthracene, tetracyanoquinodimethane (TCNQ), and polyparaphenylene vinylene (PPV).

FIG. 8 is an example of the block diagram of a display device of one embodiment of the present invention. A display device 5000 includes a display part 5001, a distortion sensor part 5002, a touch sensor part 5009, a circuit 5010, a circuit 5020, a circuit 5030, a first memory device 5040, and a second memory device 5050. Note that a structure may be employed in which components other than the display part 5001, the distortion sensor part 5002, and the touch sensor part are not provided in the display device 5000 and externally provided. To the display device 5000, various circuits such as a control circuit, an arithmetic circuit, and a power supply circuit that are not shown in the drawing, and a memory circuit that is different from that in the above can be connected.

Here, the circuit 5010 can have a function of controlling the display part 5001. The circuit 5020 can have a function of performing processing regarding information to be displayed on the display part 5001. The circuit 5030 can have a function of controlling the distortion sensor part 5002 and the touch sensor part 5009. Note that circuits for controlling the distortion sensor part 5002 and the touch sensor part 5009 may be provided. The first memory device 5040 and the second memory device 5050 can each have a function of storing data on information to be displayed on the display part 5001 (the data is hereinafter referred to as display data). The first memory device 5040 may be a reproducing device which reads the display data from a memory medium.

First, a signal detected by the distortion sensor part 5002 and/or the touch sensor part 5009 in the display part 5001 having flexibility is input to the circuit 5020 through the circuit 5030.

The circuit 5020 reads necessary display data from the first memory device 5040 depending on the signal. Part of the display data can be stored in the second memory device 5050 and read from the second memory device 5050 as needed. Furthermore, data input by a user can be stored in the second memory device 5050. The supply of power to the display part 5001 can be controlled depending on the signal detected by the distortion sensor part 5002.

The circuit 5020 can be connected to a communication device 5060. Thus, display data can be read from the outside through the communication device 5060, and display data or data input by a user can be output to the outside through the communication device 5060.

Display data read by the circuit 5020 is input to the circuit 5010, and an image based on the display data is displayed on the display part 5001.

The repetition of the above-described operation can achieve linkage between a display function and the action of bending and/or touching the display device, so that the display device can be operated by an action similar to that of reading a book.

Application modes of the display device of one embodiment of the present invention are described. FIG. 9A shows an example of the display device 5000 of one embodiment of the present invention which is opened to have a substantially flat surface. The display part 5001 can display, for example, time 5101, an icon 5102 linked to the start of software, text information 5103, and an image 5104. By using a touch sensor included in the display part 5001, the icon 5102 can be operated and screen switching can be performed, for example. That is, the display device of one embodiment of the present invention can be used as an information terminal.

Next, one mode of the display device 5000 which is used as an electronic book is described. In a state where the display device 5000 is opened to have a flat surface like the state shown in FIG. 9A, information selected by a user can be displayed on the entire display part 5001 as shown in FIG. 9B, for example.

Next, operation when the display device 5000 is bent is described. First, when the display device 5000 is bent along the vicinity of the center, an image 5003 of edges of sheets of paper bound together is displayed on each of two opposite edges of the display part as shown in FIG. 10A. Provided that the upper drawing in FIG. 10A is a front view, the lower drawing in FIG. 10A is a top view. A bend angle of the display part 5001 on which the image 5003 is displayed may be set arbitrarily. For example, the angle can be set to approximately 100° to 175°.

The image 5003 can be displayed also by bending the edge of the display device 5000 as shown in FIG. 10B. Provided that the upper drawing in FIG. 10B is a front view, the lower drawing in FIG. 10B is a top view.

As shown in FIG. 10C, the widths of the images 5003 displayed on the right and the left sides of the display part 5001 can be made different from each other so that a user can visually recognize the rough position of a displayed page. For example, in the case where a book whose pages are turned from left to right is assumed to be read using the display device 5000, at the beginning of reading, the image 5003 having a small width is displayed on the left side of the display part 5001 while the image 5003 having a large width is displayed on the right side thereof The widths of the images 5003 on the right and the left sides can be reversed at the end of the reading.

As shown in FIG. 11A, the image 5003 can include an index 5004. Furthermore, the edge of the display device 5000 can be bent so that the display surface of the display part 5001 is convex curved as shown in FIG. 11B. In that case, the bent edge can display the image 5003 of edges of sheets of paper bound together in which the distance between the edges of the sheets of paper is larger as they are closer to the outside of the display part. The width of the image 5003 can be changed depending on the curvature of the edge of the display device 5000. For example, the larger the curvature is, the more the width of the image 5003 is increased, as in the case of a book. In the case where the curvature is small, the width of the image 5003 is decreased. In the case where the curvature is small and a bent region of a center of the display device 5000 has a small curvature, the width of the image 5003 is further decreased to be closer to the display shown in FIG. 9B.

The above-described mode of the display device 5000 shown in FIGS. 10A to 10C and FIGS. 11A and 11B resembles the shape and the visual form of a real book.

Next, an example of a method for operating the display device 5000 is described.

For example, a method for changing a page displayed on the display part 5001 is described. First, the image 5003 is displayed by any of the above-described methods. Then, a region where the image 5003 is displayed is touched with a finger or the like as shown in FIG. 12A and the finger or the like is slid, whereby a given page can be displayed. For example, images can be changed so that one page is displayed at a time by slowly sliding the finger or the like. A target page can be promptly displayed by quickly sliding the finger or the like. In the case where the index 5004 is displayed, a target page can be displayed quickly by touching a region where the index 5004 is displayed. The operation is performed using functions of the distortion sensor part 5002 and the touch sensor part 5009 in the display device 5000.

Alternatively, pages can be changed by bending the display device 5000 so that the display surface of the display part 5001 is convex curved as shown in FIG. 12B. For example, it is possible to change one page every time the action of bending and returning from the bent state is performed. Furthermore, images can be changed successively with the display device 5000 bent. The operation is performed using a function of the distortion sensor part 5002 in the display device 5000.

Note that when the image is changed, an image may be displayed which looks as if a page of a book were turned, or the image may be changed immediately. In the case of performing the above-described operation using a region where the image 5003 is displayed on the left side of the display part 5001, the image can be changed as if a user turned a page from left to right. In the case of performing the above-described operation using a region where the image 5003 is displayed on the right side of the display part 5001, the image can be changed as if a user turned a page from right to left.

In the case where the image is changed as if a page of a book were turned, the speed of changing the image can be adjusted using a bend angle of the display surface. For example, the image can be slowly changed when the display surface is bent at a relatively large bend angle (closer to a flat state) as shown in FIG. 13A, whereas the image can be promptly changed when the display surface is bent at a relatively small bend angle as shown in FIG. 13B. The operation is performed using the function of the distortion sensor part 5002 in the display device 5000.

The operation of the mode of the display device 5000 which is used as an electronic book can be described with reference to a flow chart shown in FIG. 37.

First, an image is displayed on the display part 5001 (S101). The image is selected by a user and shows a front cover of a book or a given page of a book, for example. When a user intends to change a page, the user bends the vicinity of the center or the edge of the display part 5001.

The display device 5000 determines, using a distortion sensor, whether a curvature formed by the bending action is larger than or equal to a set value (S102).

In the case where the curvature is smaller than the set value, the above-described determination of the curvature is performed repeatedly while the image displayed in S101 is maintained.

In the case where the curvature is larger than or equal to the set value, the image 5003 for operation is displayed on the edge of the display part (S103).

Next, when a finger of the user is put on the image 5003, for example, the position of the finger is detected by the touch sensor of the display device 5000 (S104).

The user moves an object such as the finger on the image 5003, or bends the edge of the display part 5001.

The position of the finger is detected again by the touch sensor of the display device 5000 using a timer or the like (S105). When the position of the finger is changed at this time, a target image is selected and the image is displayed (S107). That is, the operation of changing a page is performed.

When a change in the position of the finger is not recognized in S105, the distortion sensor determines whether the curvature is larger than or equal to a set value (S106). In the case where the curvature is larger than or equal to the set value at this time, a target image is selected and the image is displayed (S107).

In the case where the curvature is smaller than the set value in S106, the image displayed in S101 is maintained, and the process returns to S105.

After the image is changed in S107, the process returns to S101. The above-described steps are performed repeatedly while the image displayed in S107 is used as the image displayed in S101.

Note that the flow chart shown in FIG. 37 is just an example; the display device can be operated while part of the steps included in the flow chart is omitted. Alternatively, a step which is not included in the flow chart may be added.

The display device 5000 may have a program in which the steps in the above-mentioned flow chart are written. Alternatively, a control device that controls the display device 5000 may have the program. Further alternatively, the program may be stored in a memory medium.

Note that the region where the image 5003 is displayed and a function of the region may be separated from the display part 5001.

The structure described in this embodiment can be used in appropriate combination with the structure described in any of the other embodiments.

Embodiment 2

In this embodiment, the distortion sensor element and the second circuit having a function of reading the amount of change in resistance of the distortion sensor element which are described in Embodiment 1, will be described in more detail. Note that in this embodiment, the second circuit electrically connected to the distortion sensor element is called a distortion sensor circuit.

FIG. 14A illustrates an example of a distortion sensor circuit that includes, as a distortion sensor element, a variable resistor such as a metal thin film resistor. The distortion sensor circuit includes a transistor 501, a transistor 502, a variable resistor 510, and a resistor 520.

One of a source and a drain of the transistor 501 is electrically connected to a wiring 540, and the other of the source and the drain is electrically connected to one of a source and a drain of the transistor 502. The other of the source and the drain of the transistor 502 is electrically connected to a wiring 550, and a gate thereof is electrically connected to a wiring 530. One terminal of the variable resistor 510 is electrically connected to a wiring 560, and the other terminal thereof is electrically connected to one terminal of the resistor 520 and a gate of the transistor 501. The other terminal of the resistor 520 is electrically connected to a wiring 570.

Here, the wiring 530 can function as a selection signal line of the distortion sensor circuit. The wiring 540 can function as a high power supply potential line. The wiring 550 can function as an output signal line. The wiring 560 can function as a high power supply potential line. The wiring 570 can function as a low power supply potential line. Note that the wiring 560 may be a low power supply potential line and the wiring 570 may be a high power supply potential line.

Conduction and non-conduction of the transistor 501 are controlled with the potential of a node ND1, and conduction and non-conduction of the transistor 502 are controlled with the potential of the wiring 530.

For example, with the assumption that a potential Vpc2 of the wiring 540 and the initial potential Vini of the wiring 550 satisfy Vini<Vpc2, when the potential of the wiring 530 is at the “H” level and the transistor 502 is on, the potential Vout of the wiring 550 depends on whether the transistor 501 is on or off. In other words, the potential Vout of the wiring 550 depends on the potential V1 of the node ND1, which is the gate potential of the transistor 501.

The potential of the node ND1 depends on the resistance R1 of the variable resistor 510 and the resistance R2 of the resistor 520. In other words, the potential V1 of the node ND1 can be expressed by the formula below where Vex1 represents the potential of the wiring 560 and Vex2 represents the potential of the wiring 570.

$\begin{matrix} {{V\; 1} = {{\frac{R\; 2}{{R\; 1} + {R\; 2}}{Vex}\; 1} + {\frac{R\; 1}{{R\; 1} + {R\; 2}}{Vex}\; 2}}} & \left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack \end{matrix}$

According to the above formula, V1 decreases when the resistance R1 of the variable resistor 510 changes in the positive direction, and V1 increases when the resistance R1 of the variable resistor 510 changes in the negative direction. In the distortion sensor circuit, the potential corresponding to V1 is outputted to the wiring 550. Thus, the amount of distortion of the variable resistor 510 can be known from the potential outputted to the wiring 550.

Note that the distortion sensor circuit of one embodiment of the present invention may have a structure illustrated in FIG. 14B. The distortion sensor circuit in FIG. 14B is different from the distortion sensor circuit in FIG. 14A in that it includes a transistor 503. One of a source and a drain of the transistor 503 is electrically connected to one terminal of the variable resistor 510, and the other of the source and the drain is electrically connected to the wiring 560. A gate of the transistor 503 is electrically connected to the wiring 530.

The transistor 503 is on only when the potential of the wiring 530 is at the “H” level, i.e., when the distortion sensor circuit is selected. Therefore, the transistor 503 is off when the potential of the wiring 530 is at the “L” level, whereby current unnecessarily flowing between the wiring 560 and the wiring 570 can be suppressed.

FIG. 15 illustrates an example of a circuit in which a distortion sensor circuit part 91, which is similar to the circuit in FIG. 14A, and a pixel circuit part 92 including an organic EL element are combined. The pixel circuit part 92 includes a transistor 504, a transistor 505, a capacitor 610, and an organic EL element 620.

One of a source and a drain of the transistor 504 is electrically connected to a wiring 580, and the other of the source and the drain is electrically connected to a gate of the transistor 505 and one terminal of the capacitor 610. A gate of the transistor 504 is electrically connected to a wiring 590. The other terminal of the capacitor 610 and one of a source and a drain of the transistor 505 are electrically connected to the wiring 560. The other of the source and the drain of the transistor 505 is electrically connected to one terminal of the organic EL element 620, and the other terminal of the organic EL element 620 is electrically connected to the wiring 570.

In the circuit illustrated in FIG. 15, the other terminal of the organic EL element 620 and the other terminal of the resistor 520 can be electrically connected to each other.

Here, the wiring 580 can function as a signal line inputting an image signal to the pixel circuit part 92. The wiring 590 can function as a selection signal line of the pixel circuit part 92.

The transistor 504 is turned on when the potential of the wiring 590 is set at the “H” level, whereby data corresponding to the potential of the wiring 580 can be written into the node ND2. When the potential of the wiring 590 is set at the “L” level, the data in the node ND2 can be stored.

Conduction and non-conduction of the transistor 505 is controlled with the potential of the node ND2. Accordingly, whether the organic EL element 620 emits light or not can be controlled with the potential of the node ND2.

Note that the circuit may have a structure as illustrated in FIG. 16 where the distortion sensor circuit part 91, which is similar to the circuit in FIG. 14B, and the pixel circuit part 92 including the organic EL element are combined. The other terminal of the capacitor 610, one of the source and the drain of the transistor 505, and the other of the source and the drain of the transistor 503 can be electrically connected to one another.

Although one pixel circuit part 92 and one distortion sensor circuit part 91 are combined in the circuits illustrated in FIGS. 15 and 16, the plurality of pixel circuit part 92 and one distortion sensor circuit part 91 can be combined as illustrated in FIG. 17. Note that although four pixel circuit part (pixel circuit part 92 a to 92 d) are shown in FIG. 17, one embodiment of the present invention is not limited to this structure and two or more pixel circuit parts and one distortion sensor circuit part 91 can be combined. Note that as illustrated in FIG. 18, the distortion sensor circuit part 91 may include the transistor 503.

Note that the wiring 550 can be provided with a circuit having a reading function as illustrated in FIG. 19. The wiring 550 is connected to a selector 630, and a selected signal is inputted to a gate of a transistor 640. Here, a transistor 650 is a switch for resetting the gate potential of the transistor 640 to a potential supplied from a wiring 545. A signal outputted from the transistor 640 can be outputted as digital data through an amplifier 660 and an analog-digital converter 670. The wiring 545 can function as a low power supply potential line. Note that the wiring 540 may be a low power supply potential line and the wiring 545 may be a high power supply potential line when the circuit having a reading function as illustrated in FIG. 19 is provided in circuits as illustrated in FIGS. 14 to 18.

Although the pixel circuit part 92 includes the organic EL element 620 in the above examples, the pixel circuit part 92 may include a liquid crystal element 625 as illustrated in FIGS. 20 and 21. It is needless to say that the transistor 503 may be included in the circuits illustrated in FIGS. 20 and 21 as in the above-described circuits.

The structure described in this embodiment can be used in appropriate combination with the structure described in any of the other embodiments.

Embodiment 3

In this embodiment, a transistor that can be used for a display device of one embodiment of the present invention and a material included in the transistor will be described. The transistor described in this embodiment can be used for the transistors 350, 352, 354, 501, 502, 503, 504, 505, and the like described in the above embodiment.

FIG. 22A is a cross-sectional view of an example of a transistor that can be used in a display device of one embodiment of the present invention. The transistor includes an insulating film 915 over a substrate 900, a gate electrode layer 920, a gate insulating film 930 in which an insulating film 931 and an insulating film 932 are stacked in this order, an oxide semiconductor layer 940, and a source electrode layer 950 and a drain electrode layer 960 in contact with part of the oxide semiconductor layer 940. In addition, an insulating film 980 and an insulating film 990 may be formed over the gate insulating film 930, the oxide semiconductor layer 940, the source electrode layer 950, and the drain electrode layer 960.

The transistor of one embodiment of the present invention may include, as illustrated in FIG. 22B, a conductive film 921 that overlaps with the gate electrode layer 920 and the oxide semiconductor layer 940 and is over the insulating film 990. When the conductive film 921 is used as a second gate electrode layer (back gate), the on-state current can be increased and the threshold voltage can be controlled. To increase the on-state current, for example, the gate electrode layer 920 and the conductive film 921 are set to have the same potential, and the transistor is driven as a dual-gate transistor. Further, to control the threshold voltage, a fixed potential that is different from a potential of the gate electrode layer 920 is supplied to the conductive film 921.

The transistor of one embodiment of the present invention may have a channel-protective bottom-gate structure as illustrated in FIGS. 23A and 23B. In this structure, an insulating film 933 has a function of protecting a channel region. Thus, the insulating film 933 may be provided only in a region overlapping with the channel region or provided in not only the region but also a region other than the region as illustrated in FIGS. 23A and 23B.

The transistor of one embodiment of the present invention may have a self-aligned top-gate structure as illustrated in FIGS. 24A and 24B. In the structure in FIG. 24A, a source region 951 and a drain region 961 can be formed in the following manner: oxygen vacancies are generated by making the source electrode layer 950 and the drain electrode layer 960 be in contact with the oxide semiconductor layer 940; and the oxide semiconductor layer 940 is doped with impurities such as boron, phosphorus, or argon using the gate electrode layer 920 as a mask. In the structure in FIG. 24B, the source region 951 and the drain region 961 can be formed, instead of using the doping method, in the following manner: an insulating film 975 containing hydrogen, such as a silicon nitride film, is formed to be in contact with part of the oxide semiconductor layer 940 and the hydrogen is diffused to the part of the oxide semiconductor layer 940.

The transistor of one embodiment of the present invention may have a self-aligned top-gate structure as illustrated in FIG. 25A. In the structure in FIG. 25A, the source region 951 and the drain region 961 can be formed in the following manner: oxygen vacancies are generated by making the source electrode layer 950 and the drain electrode layer 960 be in contact with the oxide semiconductor layer 940; and the oxide semiconductor layer 940 is doped with impurities such as boron, phosphorus, or argon using the gate insulating film 930 as a mask. In the structure in FIG. 25A, the source electrode layer 950, the drain electrode layer 960, and the gate electrode layer 920 can be formed in one process.

The transistor of one embodiment of the present invention may have a self-aligned top-gate structure as illustrated in FIG. 25B. In the structure in FIG. 25B, the source region 951 and the drain region 961 can be formed by, besides the doping with impurities such as boron, phosphorus, or argon using the gate insulating film 930 as a mask, diffusion of hydrogen from the insulating film 975 such as a silicon nitride film, which contains hydrogen and is in contact with part of the oxide semiconductor layer 940, to the part of the oxide semiconductor layer 940. In the structure, the source region 951 and the drain region 961 can have lower resistance. Alternatively, a structure in which doping with the impurities is not performed or a structure without the insulating film 975 can be formed.

The transistor of one embodiment of the present invention may include a conductive film 921 overlapping with the oxide semiconductor layer 940 with the insulating film 915 interposed therebetween as illustrated in FIGS. 26A and 26B. Although FIGS. 26A and 26B illustrate examples where the conductive film 921 is provided in the transistors illustrated in FIGS. 24A and 24B, the conductive film 921 can be provided in the transistors illustrated in FIGS. 25A and 25B.

In the display device of one embodiment of the present invention, an oxide semiconductor can be used in an active layer as described above. The transistor using an oxide semiconductor layer has a higher mobility than a transistor using amorphous silicon, and is thus easily reduced in size, resulting in a reduction in the size of a pixel. The transistor using an oxide semiconductor layer enables a flexible display device to have high reliability. Note that one embodiment of the present invention is not limited thereto. An active layer may include a semiconductor other than an oxide semiconductor depending on the case or condition.

Note that in the cross-sectional structures of the transistors illustrated in FIGS. 22A and 22B and FIGS. 23A and 23B, the width of the gate electrode layer 920 is preferably larger than that of the oxide semiconductor layer 940. In the display device having a backlight, the gate electrode layer functions as a light-blocking layer, and a deterioration of electrical characteristics, caused by irradiation of the oxide semiconductor layer 940 with light, can be suppressed. In a display device including an organic EL element or the like, a gate electrode layer in a top-gate transistor can function as a light-blocking layer.

Next, the components of the transistor of one embodiment of the present invention will be described in detail.

The substrate 900 can be formed using a material that can be used for the substrate 41 and the substrate 42 described in Embodiment 1. Note that the substrate 900 corresponds to the substrate 41 in Embodiment 1.

As the insulating film 915, for example, a single layer of a silicon oxide film, a silicon oxynitride film, a silicon nitride film, or a silicon nitride oxide film, or a stacked layer including any of the above films can be used. The insulating film 915 corresponds to the insulating film 321 a in Embodiment 1.

The gate electrode layer 920 and the conductive film 921 can be formed using a metal element selected from chromium (Cr), copper (Cu), aluminum (Al), gold (Au), silver (Ag), zinc (Zn), molybdenum (Mo), tantalum (Ta), titanium (Ti), tungsten (W), manganese (Mn), nickel (Ni), iron (Fe), and cobalt (Co), an alloy including the above metal element, an alloy in which any of the above metal elements are combined, or the like. Furthermore, the gate electrode layer 920 may have a single-layer structure or a stacked structure of two or more layers.

Alternatively, the gate electrode layer 920 and the conductive film 921 can be formed using a light-transmitting conductive material such as indium tin oxide, indium oxide containing tungsten oxide, indium zinc oxide containing tungsten oxide, indium oxide containing titanium oxide, indium tin oxide containing titanium oxide, indium zinc oxide, indium tin oxide to which silicon oxide is added, or graphene. A layered structure formed using the above light-transmitting conductive material and the above metal element can also be employed.

Further, an In-Ga-Zn-based oxynitride semiconductor film, an In-Sn-based oxynitride semiconductor film, an In-Ga-based oxynitride semiconductor film, an In-Zn-based oxynitride semiconductor film, a Sn-based oxynitride semiconductor film, an In-based oxynitride semiconductor film, a film of metal nitride (such as InN or ZnN), or the like may be provided between the gate electrode layer 920 and the insulating film 932.

As each of the insulating films 931 and 932 functioning as the gate insulating film 930, an insulating layer including at least one of the following films formed by a plasma enhanced chemical vapor deposition (PECVD) method, a sputtering method, or the like can be used: a silicon oxide film, a silicon oxynitride film, a silicon nitride oxide film, a silicon nitride film, an aluminum oxide film, a hafnium oxide film, an yttrium oxide film, a zirconium oxide film, a gallium oxide film, a tantalum oxide film, a magnesium oxide film, a lanthanum oxide film, a cerium oxide film, and a neodymium oxide film. Note that instead of a stacked structure of the insulating films 931 and 932, the gate insulating film 930 may be an insulating film of a single layer formed using a material selected from the above or an insulating film of three or more layers.

Note that the insulating film 932 that is in contact with the oxide semiconductor layer 940 functioning as a channel formation region of the transistor is preferably an oxide insulating film and preferably has a region (oxygen-excess region) containing oxygen in excess of the stoichiometric composition. In other words, the insulating film 932 is an insulating film from which oxygen can be released. In order to provide the oxygen-excess region in the insulating film 932, the insulating film 932 is formed in an oxygen atmosphere, for example. Alternatively, oxygen may be introduced into the deposited insulating film 932 to provide the oxygen-excess region therein. Oxygen can be introduced by an ion implantation method, an ion doping method, a plasma immersion ion implantation method, plasma treatment, or the like.

In the case where hafnium oxide is used for the insulating films 931 and 932, the following effect is attained. Hafnium oxide has higher dielectric constant than silicon oxide and silicon oxynitride. Therefore, when hafnium oxide is used, a thickness can be made larger than when silicon oxide is used; thus, leakage current due to tunnel current can be low.

In this embodiment, a silicon nitride film is formed as the insulating film 931, and a silicon oxide film is formed as the insulating film 932. A silicon nitride film has a higher dielectric constant than a silicon oxide film and needs a larger thickness for capacitance equivalent to that of the silicon oxide. Thus, when a silicon nitride film is used for the gate insulating film 930 of the transistor, the physical thickness of the insulating film can be increased. From the above, the electrostatic breakdown of the transistor can be prevented by improving the withstand voltage of the transistor.

The oxide semiconductor layer 940 is typically formed using an In—Ga oxide, an In—Zn oxide, or an In-M-Zn oxide (M is Ti, Ga, Y, Zr, La, Ce, Nd, Sn, or Hf). In particular, an In-M-Zn oxide (M is Ti, Ga, Y, Zr, La, Ce, Nd, Sn, or Hf) is preferably used for the oxide semiconductor layer 940.

In the case where the oxide semiconductor layer 940 is an In-M-Zn oxide (M is Ti, Ga, Y, Zr, La, Ce, Nd, Sn, or Hf), it is preferable that the atomic ratio of metal elements of a sputtering target used for forming a film of the In-M-Zn oxide satisfy In and Zn M. The sputtering target is preferably polycrystalline. As the atomic ratio of metal elements of such a sputtering target, In:M:Zn=1:1:1, In:M:Zn=5:5:6, In:M:Zn=3:1:2, In:M:Zn=2:1:3, and the like are preferable. Note that the atomic ratio of metal elements in the formed oxide semiconductor layer 940 varies from the above atomic ratio of metal elements of the sputtering target within a range of ±40% as an error.

In the case of using an In-M-Zn oxide for the oxide semiconductor layer 940, when Zn and O are eliminated from consideration, the proportion of In and the proportion of M are greater than 25 atomic % and less than 75 atomic %, respectively, preferably greater than 34 atomic % and less than 66 atomic %, respectively.

The energy gap of the oxide semiconductor layer 940 is 2 eV or more, preferably 2.5 eV or more, and more preferably 3 eV or more. In this manner, the amount of off-state current of a transistor can be reduced by using an oxide semiconductor having a wide energy gap.

The oxide semiconductor layer 940 has a thickness greater than or equal to 3 nm and less than or equal to 200 nm, preferably 3 nm to 100 nm, and further preferably 3 nm to 50 nm.

An oxide semiconductor layer with low carrier density is used as the oxide semiconductor layer 940. For example, an oxide semiconductor layer whose carrier density is lower than or equal to 1×10¹⁷/cm³, preferably lower than or equal to 1×10¹⁵/cm³, further preferably lower than or equal to 1×10¹³/cm³, still further preferably lower than or equal to 1×10¹¹/cm³ is used as the oxide semiconductor layer 940.

However, the composition is not limited to those described above, and a material having the appropriate composition may be used depending on required semiconductor characteristics and electrical characteristics of the transistor (e.g., field-effect mobility and threshold voltage). Further, in order to obtain the required semiconductor characteristics of the transistor, it is preferable that the carrier density, the impurity concentration, the defect density, the atomic ratio of a metal element to oxygen, the interatomic distance, the density, and the like of the oxide semiconductor layer 940 be set to appropriate values.

Further, in the oxide semiconductor layer, hydrogen, nitrogen, carbon, silicon, and metal elements except for main components are impurities. For example, hydrogen and nitrogen form donor levels to increase the carrier density. Silicon forms impurity states in the oxide semiconductor layer. The impurity state becomes a trap, which might deteriorate the electrical characteristics of the transistor. It is preferable to reduce the concentration of the impurities in the oxide semiconductor layer and at interfaces with other layers.

Note that stable electrical characteristics can be effectively imparted to a transistor in which an oxide semiconductor layer serves as a channel by reducing the concentration of impurities in the oxide semiconductor layer to make the oxide semiconductor layer intrinsic or substantially intrinsic. The term “substantially intrinsic” refers to the state where an oxide semiconductor layer has a carrier density lower than 1×10¹⁷/cm³, preferably lower than 1×10¹⁵/cm³, further preferably lower than 1×10¹³/cm³.

In order to make the oxide semiconductor layer intrinsic or substantially intrinsic, in SIMS (secondary ion mass spectrometry), for example, the concentration of silicon at a certain depth of the oxide semiconductor layer or in a region of the oxide semiconductor layer is lower than 1×10¹⁹ atoms/cm³, preferably lower than 5×10¹⁸ atoms/cm³, more preferably lower than 1×10¹⁸ atoms/cm³. Further, the concentration of hydrogen at a certain depth of the oxide semiconductor layer or in a region of the oxide semiconductor layer is lower than or equal to 2×10²⁰ atoms/cm³, preferably lower than or equal to 5×10¹⁹ atoms/cm³, further preferably lower than or equal to 1×10¹⁹ atoms/cm³, still further preferably lower than or equal to 5×10¹⁸ atoms/cm³. Further, the concentration of nitrogen at a certain depth of the oxide semiconductor layer or in a region of the oxide semiconductor layer is lower than 5×10¹⁹ atoms/cm³, preferably lower than or equal to 5×10¹⁸ atoms/cm³, further preferably lower than or equal to 1×10¹⁸ atoms/cm³, still further preferably lower than or equal to 5×10¹⁷ atoms/cm³.

In the case where the oxide semiconductor layer includes crystals, high concentration of silicon or carbon might reduce the crystallinity of the oxide semiconductor layer. In order not to lower the crystallinity of the oxide semiconductor layer, for example, the concentration of silicon at a certain depth of the oxide semiconductor layer or in a region of the oxide semiconductor layer is lower than 1×10¹⁹ atoms/cm³, preferably lower than 5×10¹⁸ atoms/cm³, further preferably lower than 1×10¹⁸ atoms/cm³. Further, the concentration of carbon at a certain depth of the oxide semiconductor layer or in a region of the oxide semiconductor layer is lower than 1×10¹⁹ atoms/cm³, preferably lower than 5×10¹⁸ atoms/cm³, further preferably lower than 1×10¹⁸ atoms/cm³, for example.

Various experiments can prove low off-state current of a transistor including a highly purified oxide semiconductor layer for a channel formation region. For example, even when an element has a channel width of 1×10⁶ μm and a channel length of 10 μm, off-state current can be less than or equal to the measurement limit of a semiconductor parameter analyzer, i.e., less than or equal to 1×10⁻¹³ A, at voltage (drain voltage) between the source electrode and the drain electrode of from 1 V to 10 V. In this case, it can be seen that the off-state current normalized on the channel width of the transistor is lower than or equal to 100 zA/μm. In addition, a capacitor and a transistor are connected to each other and the off-state current is measured with a circuit in which charge flowing into or from the capacitor is controlled by the transistor. In the measurement, a highly purified oxide semiconductor layer is used for a channel formation region of the transistor, and the off-state current of the transistor is measured by a change in the amount of electric charge of the capacitor per unit time. As a result, it is found that in the case where the voltage between the source electrode and the drain electrode of the transistor is 3 V, lower off-state current of several tens of yoctoamperes per micrometer (yA/μm) can be obtained. Accordingly, the off-state current of the transistor including a channel formation region formed of the highly purified oxide semiconductor layer is considerably lower than that of a transistor including silicon having crystallinity.

For the source electrode layer 950 and the drain electrode layer 960, a conductive film having properties of extracting oxygen from the oxide semiconductor layer is preferably used. For example, Al, Cr, Cu, Ta, Ti, Mo, W, Ni, Mn, Nd, or Sc can be used. An alloy or a conductive nitride of any of these materials can also be used. A stack including a plurality of materials selected from these materials, alloys of these materials, and conductive nitrides of these materials can also be used. Typically, it is preferable to use Ti, which is particularly easily bonded to oxygen, or W, which has a high melting point and thus allows subsequent process temperatures to be relatively high. Alternatively, Cu or a Cu—X alloy (X indicates Mn, Ni, Cr, Fe, Co, Mo, Ta, or Ti), which has low resistance may be used. Further alternatively, a stacked layer including any of the above materials and Cu or a Cu—X alloy may be used.

In the case of using a Cu—X alloy (X indicates Mn, Ni, Cr, Fe, Co, Mo, Ta, or Ti), a covering film is formed in a region in contact with the oxide semiconductor layer or a region in contact with an insulating film by heat treatment, in some cases. The covering film includes a compound containing X Examples of a compound containing X include an oxide of X, an In—X oxide, a Ga—X oxide, an In—Ga—X oxide, and In—Ga—Zn—X oxide. When the covering film is formed, the covering film functions as a blocking film, and Cu in the Cu—X alloy film can be prevented from entering the oxide semiconductor layer.

By the conductive film capable of extracting oxygen from the oxide semiconductor layer, oxygen in the oxide semiconductor layer is released to form oxygen vacancies in the oxide semiconductor layer. Hydrogen slightly contained in the layer and the oxygen vacancy are bonded to each other, whereby the region is markedly changed to an n-type region. Accordingly, the n-type regions can serve as a source or a drain region of the transistor.

The insulating films 980 and 990 each have a function of a protective insulating film. The insulating film 980 is formed using an oxide insulating film containing oxygen in excess of that in the stoichiometric composition. Part of oxygen is released by heating from the oxide insulating film containing oxygen in excess of that in the stoichiometric composition. The oxide insulating film containing oxygen in excess of that in the stoichiometric composition is an oxide insulating film of which the amount of released oxygen converted into oxygen atoms is greater than or equal to 1.0×10¹⁸ atoms/cm³, preferably greater than or equal to 3.0×10²⁰ atoms/cm³ in TDS analysis in which heat treatment is performed such that a temperature of a film surface is higher than or equal to 100° C. and lower than or equal to 700° C., preferably higher than or equal to 100° C. and lower than or equal to 500° C.

Silicon oxide, silicon oxynitride, or the like with a thickness greater than or equal to 30 nm and less than or equal to 500 nm, preferably greater than or equal to 50 nm and less than or equal to 400 nm can be used as the insulating film 980.

Further, it is preferable that the amount of defects in the insulating film 980 be small, typically the spin density of a signal which appears at g=2.001 originating from a dangling bond of silicon, be lower than 1.5×10¹⁸ spins/cm³, further preferably lower than or equal to 1×10¹⁸ spins/cm³ by ESR measurement. Note that the insulating film 980 is provided more apart from the oxide semiconductor layer 940 than the insulating film 970 is; thus, the insulating film 980 may have higher defect density than the insulating film 970.

The insulating film 990 has a function of blocking oxygen, hydrogen, water, an alkali metal, an alkaline earth metal, or the like. With the insulating film 990, oxygen diffusion from the oxide semiconductor layer 940 to the outside and entry of hydrogen, water, or the like from the outside to the oxide semiconductor layer 940 can be prevented. As the insulating film 990, a nitride insulating film can be used, for example. The nitride insulating film is formed using silicon nitride, silicon nitride oxide, aluminum nitride, aluminum nitride oxide, or the like. Note that instead of the nitride insulating film having a blocking effect against oxygen, hydrogen, water, alkali metal, alkaline earth metal, and the like, an oxide insulating film having a blocking effect against oxygen, hydrogen, water, and the like, may be provided. The oxide insulating film having a blocking effect against oxygen, hydrogen, water, and the like is formed using aluminum oxide, aluminum oxynitride, gallium oxide, gallium oxynitride, yttrium oxide, yttrium oxynitride, hafnium oxide, hafnium oxynitride, or the like.

Note that the oxide semiconductor layer 940 may have a structure in which a plurality of oxide semiconductor layers are stacked. For example, as in a transistor illustrated in FIG. 27A, stacked layers of a first oxide semiconductor layer 941 a and a second oxide semiconductor layer 941 b may constitute the oxide semiconductor layer 940. The first oxide semiconductor layer 941 a and the second oxide semiconductor layer 941 b may include metal oxides having different atomic ratios. For example, one of the oxide semiconductor layers may include one of an oxide containing two kinds of metals, an oxide containing three kinds of metals, and an oxide containing four kinds of metals, and the other of the oxide semiconductor layers may include another one of the oxide containing two kinds of metals, the oxide containing three kinds of metals, and the oxide containing four kinds of metals.

Alternatively, the first oxide semiconductor layer 941 a and the second oxide semiconductor layer 941 b may include the same constituent elements with different atomic ratios. For example, one of the oxide semiconductor layers may contain In, Ga, and Zn at an atomic ratio of 1:1:1, 5:5:6, 3:1:2, or 2:1:3 and the other of the oxide semiconductor layers may contain In, Ga, and Zn at an atomic ratio of 1:3:2, 1:3:4, 1:3:6, 1:4:5, 1:6:4, or 1:9:6. Note that the atomic ratio of each oxide semiconductor layer varies within a range of ±40% of the above atomic ratio as an error.

In the above, one of the oxide semiconductor layers, which is closer to the gate electrode (the oxide semiconductor layer on the channel side), has an atomic ratio of In Ga (in the atomic ratio, In is greater than or equal to Ga); and the other oxide semiconductor layer, which is farther from the gate electrode (the oxide semiconductor layer on the back channel side), has an atomic ratio of In<Ga. In that case, a transistor with a high field-effect mobility can be manufactured. On the other hand, when the oxide semiconductor layer on the channel side has an atomic ratio of In<Ga and the oxide semiconductor layer on the back channel side has an atomic ratio of In Ga (in the atomic ratio, In is greater than or equal to Ga), the amount of change in the threshold voltage of a transistor due to change over time or a reliability test can be reduced.

Further alternatively, the semiconductor film of the transistor may have a three-layer structure of a first oxide semiconductor layer, a second oxide semiconductor layer, and a third oxide semiconductor layer. In that case, the first to third oxide semiconductor layers may include the same constituent elements with different atomic ratios. A transistor including a three-layer semiconductor film will be described with reference to FIG. 27B and FIGS. 28A and 28B. Note that a structure in which a semiconductor film has a stacked structure can be employed for other transistors described in this embodiment.

Each of the transistors illustrated in FIG. 27B and FIGS. 28A and 28B includes a first oxide semiconductor layer 942 a, a second oxide semiconductor layer 942 b, and a third oxide semiconductor layer 942 c which are stacked in this order from a gate insulating film side.

The first oxide semiconductor layer 942 a and the third oxide semiconductor layer 942 c are formed using a material represented by InM_(1x)Zn_(y)O_(z) (x≥1 (x is greater than or equal to 1), y>1, z>0, M₁=Ga, Hf, or the like). The second oxide semiconductor layer 942 b is formed using a material which can be represented by InM_(2x)Zn_(y)O_(z) (x≥1 (x is greater than or equal to 1), y≥x (y is greater than or equal to x), z>0, M₂=Ga, Sn, or the like).

Materials of the first to third oxide semiconductor layers are selected as appropriate so as to form a well-shaped structure in which the conduction band minimum in the second oxide semiconductor layer 942 b is deeper from the vacuum level than the conduction band minimum in the first and third oxide semiconductor layers 942 a and 942 c.

For example, the first oxide semiconductor layer 942 a and the third oxide semiconductor layer 942 c may each have an atomic ratio of In:Ga:Zn=1:1:1, 1:3:2, 1:3:4, 1:3:6, 1:4:5, 1:6:4, or 1:9:6; the second oxide semiconductor layer 942 b may have an atomic ratio of In:Ga:Zn=1:1:1, 5:5:6, 3:1:2, or 2:1:3.

Since the first to third oxide semiconductor layers 942 a to 942 c include the same constituent elements, the second oxide semiconductor layer 942 b has few defect states (trap states) at the interface with the first oxide semiconductor layer 942 a. Specifically, the defect states (trap states) are fewer than those at the interface between the gate insulating film and the first oxide semiconductor layer 942 a. For this reason, when the oxide semiconductor layers are stacked in the above manner, the amount of change in the threshold voltage of a transistor due to a change over time or a reliability test can be reduced.

Further, a well-shaped structure is preferably formed in which the conduction band minimum in the second oxide semiconductor layer 942 b is deeper from the vacuum level than the conduction band minimum in the first and third oxide semiconductor layers 942 a and 942 c. When materials of the first to third oxide semiconductor layers are selected as appropriate, the field-effect mobility of the transistor can be increased and the amount of change in the threshold voltage of the transistor due to change over time or a reliability test can be reduced.

Further, the first to third oxide semiconductor layers 942 a to 942 c may be formed using oxide semiconductors having different crystallinities. Note that at least the second oxide semiconductor layer 942 b that can function as a channel formation region is preferably a film with crystallinity, further preferably a film in which c-axes are aligned in a direction substantially perpendicular to a surface.

The top-gate transistor illustrated in FIG. 28A or the like preferably has any of cross-sectional structures illustrated in FIG. 29A in the channel width direction of a channel formation region. In each of the above structures, the gate electrode layer 920 electrically surrounds the oxide semiconductor layer 940 in the channel width direction. This structure increases the on-state current. Such a transistor structure is referred to as a surrounded channel (s-channel) structure.

In the structure including the conductive film 921 as illustrated in FIGS. 26A and 26B, the gate electrode layer 920 and the conductive film 921 may be connected to each other through a contact hole, as illustrated in FIG. 29B, so as to have the same potential.

Furthermore, top-view structures of the source electrode layer 950 and the drain electrode layer 960 of the transistor of one embodiment of the present invention can be as illustrated in FIGS. 30A and 30B. Note that FIGS. 30A and 30B each illustrate only the oxide semiconductor layer 940, the source electrode layer 950, and the drain electrode layer 960. As shown in FIG. 30A, the width (W_(SD)) of each of the source electrode layer 950 and the drain electrode layer 960 may be larger than the width (W_(OS)) of the oxide semiconductor layer 940. Alternatively, W_(SD) may be smaller than Wos as shown in FIG. 30B. When W_(OS)≥W_(SD) (W_(SD) is less than or equal to W_(OS)) is satisfied, a gate electric field is easily applied to the entire oxide semiconductor layer 940, so that electrical characteristics of the transistor can be improved.

Although the variety of films such as the metal films, the semiconductor films, and the inorganic insulating films which are described in this embodiment typically can be formed by a sputtering method or a plasma CVD method, such films may be formed by another method, e.g., a thermal CVD method. A metal organic chemical vapor deposition (MOCVD) method or an atomic layer deposition (ALD) method may be employed as an example of a thermal CVD method.

A thermal CVD method has an advantage that no defect due to plasma damage is generated since it does not utilize plasma for forming a film.

Deposition by a thermal CVD method may be performed in such a manner that a source gas and an oxidizer are supplied to a chamber at a time, the pressure in the chamber is set to an atmospheric pressure or a reduced pressure, and reaction is caused in the vicinity of the substrate or over the substrate.

Deposition by an ALD method may be performed in such a manner that the pressure in a chamber is set to an atmospheric pressure or a reduced pressure, source gases for reaction are sequentially introduced into the chamber, and then the sequence of the gas introduction is repeated. For example, two or more kinds of source gases are sequentially supplied to the chamber by switching the respective switching valves (also referred to as high-speed valves) such that the source gases are not mixed. For example, a first source gas is introduced, an inert gas (e.g., argon or nitrogen) or the like is introduced at the same time as or after the introduction of the first gas, and then a second source gas is introduced. Note that in the case where the first source gas and the inert gas are introduced at a time, the inert gas serves as a carrier gas, and the inert gas may also be introduced at the same time as the introduction of the second source gas. Alternatively, the first source gas may be exhausted by vacuum evacuation instead of the introduction of the inert gas, and then the second source gas may be introduced. The first source gas is adsorbed on the surface of the substrate to form a first layer; then, the second source gas is introduced to react with the first layer; as a result, a second layer is stacked over the first layer, so that a thin film is formed. The sequence of the gas introduction is controlled and repeated plural times until a desired thickness is obtained, whereby a thin film with excellent step coverage can be formed. The thickness of the thin film can be adjusted by the number of repetition times of the sequence of the gas introduction; therefore, an ALD method makes it possible to adjust a thickness accurately and thus is suitable for manufacturing a minute FET.

The variety of films such as the metal film, the semiconductor film, and the inorganic insulating film which have been disclosed in the embodiments can be formed by a thermal CVD method such as a MOCVD method or an ALD method. For example, in the case where an In—Ga—Zn—O film is formed, trimethylindium, trimethylgallium, and dimethylzinc can be used. Note that the chemical formula of trimethylindium is In(CH₃)₃. The chemical formula of trimethylgallium is Ga(CH₃)₃. The chemical formula of dimethylzinc is Zn(CH₃)₂. Without limitation to the above combination, triethylgallium (chemical formula: Ga(C₂H₅)₃) can be used instead of trimethylgallium and diethylzinc (chemical formula: Zn(C₂H₅)₂) can be used instead of dimethylzinc.

For example, in the case where a hafnium oxide film is formed by a deposition apparatus using an ALD method, two kinds of gases, i.e., ozone (O₃) as an oxidizer and a source gas which is obtained by vaporizing liquid containing a solvent and a hafnium precursor compound (hafnium alkoxide or hafnium amide such as tetrakis(dimethylamide)hafnium (TDMAH)) are used. Note that the chemical formula of tetrakis(dimethylamide)hafnium is Hf[N(CH₃)₂]₄. Examples of another material liquid include tetrakis(ethylmethylamide)hafnium.

For example, in the case where an aluminum oxide film is formed using a deposition apparatus employing ALD, two kinds of gases, e.g., H₂O as an oxidizer and a source gas which is obtained by vaporizing a solvent and liquid containing an aluminum precursor compound (e.g., trimethylaluminum (TMA)) are used. Note that the chemical formula of trimethylaluminum is Al(CH₃)₃. Examples of another material liquid include tris(dimethylamide)aluminum, triisobutylaluminum, and aluminum tris(2,2,6,6-tetramethyl-3,5-heptanedionate).

For example, in the case where a silicon oxide film is formed by a deposition apparatus using ALD, hexachlorodisilane is adsorbed on a surface where a film is to be formed, chlorine contained in the adsorbate is removed, and radicals of an oxidizing gas (e.g., O₂ or dinitrogen monoxide) are supplied to react with the adsorbate.

For example, in the case where a tungsten film is formed using a deposition apparatus employing ALD, a WF₆ gas and a B₂H₆ gas are sequentially introduced plural times to form an initial tungsten film, and then a WF₆ gas and an H₂ gas are introduced at a time, so that a tungsten film is formed. Note that an SiH₄ gas may be used instead of a B₂H₆ gas.

For example, in the case where an oxide semiconductor film, e.g., an In—Ga—Zn—O film is formed using a deposition apparatus employing ALD, an In(CH₃)₃ gas and an O₃ gas are sequentially introduced plural times to form an In—O layer, a Ga(CH₃)₃ gas and an O₃ gas are introduced at a time to form a GaO layer, and then a Zn(CH₃)₂ gas and an O₃ gas are introduced at a time to form a ZnO layer. Note that the order of these layers is not limited to this example. A mixed compound layer such as an In—Ga—O layer, an In—Zn—O layer, or a Ga—Zn—O layer may be formed by mixing of these gases. Note that although an H₂O gas which is obtained by bubbling with an inert gas such as Ar may be used instead of an O₃ gas, it is preferable to use an O₃ gas, which does not contain H. Further, instead of an In(CH₃)₃ gas, an In(C₂H₅)₃ gas may be used. Instead of a Ga(CH₃)₃ gas, a Ga(C₂H₅)₃ gas may be used. Further, a Zn(CH₃)₂ gas may be used.

The structure described in this embodiment can be used in appropriate combination with the structure described in any of the other embodiments.

Embodiment 4

A structure of an oxide semiconductor film which can be used for one embodiment of the present invention is described below.

In this specification, the term “parallel” indicates that the angle formed between two straight lines is greater than or equal to −10° and less than or equal to 10°, and accordingly also includes the case where the angle is greater than or equal to −5° and less than or equal to 5°. In addition, the term “perpendicular” indicates that the angle formed between two straight lines is greater than or equal to 80° and less than or equal to 100°, and accordingly also includes the case where the angle is greater than or equal to 85° and less than or equal to 95°.

In this specification, trigonal and rhombohedral crystal systems are included in a hexagonal crystal system.

An oxide semiconductor film is classified roughly into a single-crystal oxide semiconductor film and a non-single-crystal oxide semiconductor film. The non-single-crystal oxide semiconductor film includes any of a c-axis aligned crystalline oxide semiconductor (CAAC-OS) film, a polycrystalline oxide semiconductor film, a microcrystalline oxide semiconductor film, an amorphous oxide semiconductor film, and the like.

First, a CAAC-OS film is described.

The CAAC-OS film is one of oxide semiconductor films having a plurality of c-axis aligned crystal parts.

When observing the CAAC-OS film in a combined analysis image of a bright-field image and a diffraction pattern with the use of a transmission electron microscope (TEM) (the combined analysis image is also referred to as a high-resolution TEM image), a plurality of crystal parts can be found. However, in the high-resolution TEM image, a boundary between crystal parts, that is, a grain boundary is not clearly observed. Thus, in the CAAC-OS film, a reduction in electron mobility due to the grain boundary is less likely to occur.

According to the high-resolution cross-sectional TEM image of the CAAC-OS film observed in a direction substantially parallel to a sample surface, metal atoms are arranged in a layered manner in the crystal parts. Each metal atom layer has a morphology reflecting unevenness of a surface over which the CAAC-OS film is formed (hereinafter, a surface over which the CAAC-OS film is formed is referred to as a formation surface) or a top surface of the CAAC-OS film, and is arranged parallel to the formation surface or the top surface of the CAAC-OS film.

On the other hand, according to the high-resolution planar TEM image of the CAAC-OS film observed in a direction substantially perpendicular to the sample surface, metal atoms are arranged in a triangular or hexagonal configuration in the crystal parts. However, there is no regularity of arrangement of metal atoms between different crystal parts.

A CAAC-OS film is subjected to structural analysis with an X-ray diffraction (XRD) apparatus. For example, when the CAAC-OS film including an InGaZnO₄ crystal is analyzed by an out-of-plane method, a peak appears frequently when the diffraction angle (2θ) is around 31°. This peak is derived from the (009) plane of the InGaZnO₄ crystal, which indicates that crystals in the CAAC-OS film have c-axis alignment, and that the c-axes are aligned in a direction substantially perpendicular to the formation surface or the top surface of the CAAC-OS film.

Note that when the CAAC-OS film with an InGaZnO₄ crystal is analyzed by an out-of-plane method, a peak of 2θ may also be observed at around 36°, in addition to the peak of 2θ at around 31°. The peak at 2θ of around 36° indicates that a crystal having no c-axis alignment is included in part of the CAAC-OS film. It is preferable that in the CAAC-OS film, a peak of 2θ appear at around 31° and a peak of 2θ not appear at around 36°.

The CAAC-OS film is an oxide semiconductor film having low impurity concentration. The impurity is an element other than the main components of the oxide semiconductor film, such as hydrogen, carbon, silicon, or a transition metal element. In particular, an element that has higher bonding strength to oxygen than a metal element included in the oxide semiconductor film, such as silicon, disturbs the atomic arrangement of the oxide semiconductor film by depriving the oxide semiconductor film of oxygen and causes a decrease in crystallinity. Further, a heavy metal such as iron or nickel, argon, carbon dioxide, or the like has a large atomic radius (molecular radius), and thus disturbs the atomic arrangement of the oxide semiconductor film and causes a decrease in crystallinity when it is contained in the oxide semiconductor film. Note that the impurity contained in the oxide semiconductor film might serve as a carrier trap or a carrier generation source.

The CAAC-OS film is an oxide semiconductor film having a low density of defect states. In some cases, oxygen vacancy in the oxide semiconductor film serves as a carrier trap or serves as a carrier generation source when hydrogen is captured therein.

The state in which impurity concentration is low and density of defect states is low (the number of oxygen vacancies is small) is referred to as a “highly purified intrinsic” or “substantially highly purified intrinsic” state. A highly purified intrinsic or substantially highly purified intrinsic oxide semiconductor film has few carrier generation sources, and thus can have a low carrier density. Thus, the transistor including the oxide semiconductor film rarely has negative threshold voltage (is rarely normally on). The highly purified intrinsic or substantially highly purified intrinsic oxide semiconductor film has few carrier traps. Accordingly, the transistor including the oxide semiconductor film has little variation in electrical characteristics and high reliability. Electric charge trapped by the carrier traps in the oxide semiconductor film takes a long time to be released, and might behave like fixed electric charge. Thus, the transistor which includes the oxide semiconductor film having high impurity concentration and a high density of defect states has unstable electrical characteristics in some cases.

With the use of the CAAC-OS film in a transistor, variation in the electrical characteristics of the transistor due to irradiation with visible light or ultraviolet light is small.

Next, a microcrystalline oxide semiconductor film is described.

A microcrystalline oxide semiconductor film has a region where a crystal part is observed in a high-resolution TEM image and a region where a crystal part is not clearly observed in a high-resolution TEM image. In most cases, a crystal part in the microcrystalline oxide semiconductor film is greater than or equal to 1 nm and less than or equal to 100 nm, or greater than or equal to 1 nm and less than or equal to 10 nm. A microcrystal with a size greater than or equal to 1 nm and less than or equal to 10 nm, or a size greater than or equal to 1 nm and less than or equal to 3 nm is specifically referred to as nanocrystal (nc). An oxide semiconductor film including nanocrystal is referred to as an nc-OS (nanocrystalline oxide semiconductor) film. In a high-resolution TEM image of the nc-OS film, for example, a grain boundary is not clearly observed in some cases.

In the nc-OS film, a microscopic region (for example, a region with a size greater than or equal to 1 nm and less than or equal to 10 nm, in particular, a region with a size greater than or equal to 1 nm and less than or equal to 3 nm) has a periodic atomic order. Note that there is no regularity of crystal orientation between different crystal parts in the nc-OS film. Thus, the orientation of the whole film is not observed. Accordingly, in some cases, the nc-OS film cannot be distinguished from an amorphous oxide semiconductor depending on an analysis method. For example, when the nc-OS film is subjected to structural analysis by an out-of-plane method with an XRD apparatus using an X-ray having a diameter larger than the diameter of a crystal part, a peak which shows a crystal plane does not appear. Furthermore, a diffraction pattern like a halo pattern appears in a selected-area electron diffraction pattern of the nc-OS film which is obtained by using an electron beam having a probe diameter (e.g., larger than or equal to 50 nm) larger than the diameter of a crystal part. Meanwhile, spots appear in a nanobeam electron diffraction pattern of the nc-OS film obtained by using an electron beam having a probe diameter close to, or smaller than the diameter of a crystal part. Further, in a nanobeam electron diffraction pattern of the nc-OS film, regions with high luminance in a circular (ring) pattern are shown in some cases. Also in a nanobeam electron diffraction pattern of the nc-OS film, a plurality of spots are shown in a ring-like region in some cases.

The nc-OS film is an oxide semiconductor film that has high regularity as compared to an amorphous oxide semiconductor film. Therefore, the nc-OS film has a lower density of defect states than an amorphous oxide semiconductor film. However, there is no regularity of crystal orientation between different crystal parts in the nc-OS film; hence, the nc-OS film has a higher density of defect states than the CAAC-OS film.

Next, an amorphous oxide semiconductor film is described.

The amorphous oxide semiconductor film has disordered atomic arrangement and no crystal part. For example, the amorphous oxide semiconductor film does not have a specific state as in quartz.

In the high-resolution TEM image of the amorphous oxide semiconductor film, crystal parts cannot be found.

When the amorphous oxide semiconductor film is subjected to structural analysis by an out-of-plane method with an XRD apparatus, a peak which shows a crystal plane does not appear. A halo pattern is shown in an electron diffraction pattern of the amorphous oxide semiconductor film. Further, a halo pattern is shown but a spot is not shown in a nanobeam electron diffraction pattern of the amorphous oxide semiconductor film.

Note that an oxide semiconductor film may have a structure having physical properties between the nc-OS film and the amorphous oxide semiconductor film. The oxide semiconductor film having such a structure is specifically referred to as an amorphous-like oxide semiconductor (amorphous-like OS).

In a high-resolution TEM image of the amorphous-like OS film, a void is observed in some cases. Furthermore, in the high-resolution TEM image, there are a region where a crystal part is clearly observed and a region where a crystal part is not observed. In the amorphous-like OS film, crystallization occurs by a slight amount of electron beam used for TEM observation and growth of the crystal part is found in some cases. In contrast, crystallization by a slight amount of electron beam used for TEM observation is hardly observed in the nc-OS film having good quality.

Note that the crystal part size in the amorphous-like OS film and the nc-OS film can be measured using high-resolution TEM images. For example, an InGaZnO₄ crystal has a layered structure in which two Ga—Zn—O layers are included between In—O layers. A unit cell of the InGaZnO₄ crystal has a structure in which nine layers of three In—O layers and six Ga—Zn—O layers are layered in the c-axis direction. Accordingly, the spacing between these adjacent layers is equivalent to the lattice spacing on the (009) plane (also referred to as d value). The value is calculated to 0.29 nm from crystal structure analysis. Thus, focusing on lattice fringes in the high-resolution TEM image, each of lattice fringes in which the lattice spacing therebetween is greater than or equal to 0.28 nm and less than or equal to 0.30 nm corresponds to the a-b plane of the InGaZnO₄ crystal.

Note that an oxide semiconductor film may be a stacked film including two or more films of an amorphous oxide semiconductor film, an amorphous-like OS film, a microcrystalline oxide semiconductor film, and a CAAC-OS film, for example.

The structure described in this embodiment can be used in appropriate combination with the structure described in any of the other embodiments.

Embodiment 5

In this embodiment, a display module which can be formed using a display device of one embodiment of the present invention will be described.

In a display module 8000 in FIG. 31, a touch panel 8004 connected to an FPC 8003, a display panel 8006 connected to an FPC 8005, a backlight unit 8007, a frame 8009, a printed circuit board 8010, and a battery 8011 are provided between an upper cover 8001 and a lower cover 8002.

The display device of one embodiment of the present invention can be used for, for example, the display panel 8006.

The shapes and sizes of the upper cover 8001 and the lower cover 8002 can be changed as appropriate in accordance with the sizes of the touch panel 8004 and the display panel 8006. The upper cover 8001 and the lower cover 8002 have flexibility.

The touch panel 8004 is, typically, a resistive touch panel or a capacitive touch panel and overlaps with the display panel 8006. A counter substrate (sealing substrate) of the display panel 8006 can have a touch panel function. A photosensor may be provided in each pixel of the display panel 8006 so that the touch panel 8004 can function as an optical touch panel. The touch panel 8004 may have flexibility. The function of the touch panel may be achieved by the use of the distortion sensor element of one embodiment of the present invention.

The backlight unit 8007 includes a light source 8008. Note that although a structure in which the light sources 8008 are provided over the backlight unit 8007 is illustrated in FIG. 31, one embodiment of the present invention is not limited to this structure. For example, a structure in which a light source 8008 is provided at an end of the backlight unit 8007 and a light diffusion plate is further provided may be employed. In the case where a self-luminous light-emitting element such as an organic EL element is used or the case where a reflective panel is used, the backlight unit 8007 is not necessarily provided. The backlight unit 8007 may have flexibility.

The frame 8009 protects the display panel 8006 and functions as an electromagnetic shield for blocking electromagnetic waves generated by the operation of the printed circuit board 8010. The frame 8009 can function as a radiator plate. The frame 8009 may have flexibility.

The printed circuit board 8010 has a power supply circuit and a signal processing circuit for outputting a video signal and a clock signal. As a power source for supplying power to the power supply circuit, an external commercial power source or a power source using the battery 8011 provided separately may be used. The battery 8011 can be omitted in the case of using a commercial power source. The printed circuit board 8010 may be an FPC.

The display module 8000 may be additionally provided with a member such as a polarizing plate, a retardation plate, or a prism sheet.

The structure described in this embodiment can be used in appropriate combination with the structure described in any of the other embodiments.

Embodiment 6

In this embodiment, a touch panel that can include a display device provided with the distortion sensor of one embodiment of the present invention will be described.

The display device of one embodiment of the present invention can have a structure in which a touch sensor, a display element, and a distortion sensor element are provided between a pair of substrates. The touch sensor is a capacitive type touch sensor, for example. The touch panel allows not only input by local touch on a display part but also input by bending of the display part owing to the distortion sensor element. Note that the description of the distortion sensor element in the above embodiment is not made below.

In a touch panel including a touch sensor part and a display part that overlap with each other, a parasitic capacitance is formed in some cases between a wiring or an electrode included in a capacitive type touch sensor and a wiring or an electrode included in the display part. Noise caused by operating the display element travels to the touch sensor side through the parasitic capacitance and the detection sensitivity of the touch sensor might decrease.

By sufficiently increasing the distance between the touch sensor part and the display part, the adverse effect of the noise can be avoided and the decrease in the detection sensitivity of the touch sensor can be suppressed; however, the thickness of the whole touch panel is increased in some cases.

This embodiment describes an example of using an active matrix touch sensor. The touch sensor includes a transistor and a capacitor. The transistor and the capacitor are electrically connected to each other. Note that a touch sensor without an element such as a transistor may be used for the display device of one embodiment of the present invention.

In the active matrix touch sensor of one embodiment of the present invention, an electrode of a capacitor and a read wiring can be formed in different layers. When the read wiring has a narrow width, a parasitic capacitance can be small and the adverse effect of the noise can be suppressed. Accordingly, a decrease in the detection sensitivity of the touch sensor can be suppressed. In addition, by amplifying a detection signal and outputting the amplified signal, the adverse effect of the noise can be suppressed.

An active matrix touch sensor is used in the touch panel of one embodiment of the present invention, whereby the distance between the sensor part and the display part can be reduced in the touch panel, and the touch panel can have a small thickness. Furthermore, the touch sensor and the display element can be located between two substrates, whereby the touch panel can have a small thickness. Here, using the touch sensor of one embodiment of the present invention can suppress a decrease in the detection sensitivity of the touch sensor even when the distance between the sensor part and the display part is reduced. Therefore, in one embodiment of the present invention, both a small thickness and high detection sensitivity of a touch sensor or a touch panel can be achieved. Furthermore, by using a flexible material for the pair of substrates of the touch panel, the touch panel can have flexibility. Furthermore, in one embodiment of the present invention, a touch panel with high resistance to repeated bending can be provided. Furthermore, a large-sized touch panel can be provided.

The touch sensor included in the touch panel of one embodiment of the present invention may include an oxide conductor layer as the electrode of the capacitor. In the active matrix touch sensor, a semiconductor layer and a conductive film of the transistor and the electrode of the capacitor are preferably formed in the same step. Thus, the number of steps of manufacturing the touch panel can be reduced and the cost of manufacturing the touch panel can be reduced.

Note that because the oxide conductor layer is used as the electrode of the capacitor in the touch panel of one embodiment of the present invention, viewing angle dependence is smaller than that of a touch panel using another material as the electrode of the capacitor in some cases. Furthermore, because the oxide conductor layer is used as the electrode of the capacitor in the touch panel of one embodiment of the present invention, an NTSC ratio can be higher than that of a touch panel using another material as the electrode of the capacitor in some cases.

Specifically, one embodiment of the present invention is a touch panel including a touch sensor, a light-blocking layer, and a display element. In the touch panel, the light-blocking layer is located between the touch sensor and the display element, the light-blocking layer includes a region overlapping with a transistor included in the touch sensor, and the display element includes a region overlapping with a capacitor included in the touch sensor. Note that the touch panel allows data input without contact.

The display element can be, but is not particularly limited to, an organic EL element.

<Structure Example of Touch Panel>

FIGS. 32A and 32B are projection views illustrating components of a touch panel of one embodiment of the present invention. FIG. 32A is a projection view of a touch panel 700 of one embodiment of the present invention and a sensor unit 800 included in the touch panel 700.

The touch panel 700 described in this embodiment includes a flexible input device 100 and a display part 701 (see FIGS. 32A and 32B). The flexible input device 100 is provided with a plurality of sensor units 800 arranged in matrix and including windows 14 that transmit visible light; a scan line G1 electrically connected to the plurality of sensor units 800 arranged in the row direction (shown by an arrow R in FIG. 32A); a signal line DL electrically connected to the plurality of sensor units 800 arranged in the column direction (shown by an arrow C in FIG. 32A); and a flexible base material 16 supporting the sensor units 800, the scan line G1, and the signal line DL. The display part 701 is provided with a plurality of pixels 702 overlapping with the windows 14 and arranged in matrix; and a flexible base material 710 supporting the pixels 702.

The sensor unit 800 includes a sensor element C overlapping with the windows 14 and a sensing circuit 19 electrically connected to the sensor element C (FIG. 32A).

The sensing circuit 19 is supplied with a selection signal, and supplies a sensor signal DATA in accordance with a change in capacitance of the sensor element C.

The scan line G1 can supply a selection signal. The signal line DL can supply the sensor signal DATA. The sensing circuit 19 is provided so as to overlap with a gap between the windows 14.

In addition, the touch panel 700 described in this embodiment includes a coloring layer between the sensor unit 800 and the pixel 702 overlapping with the window 14 of the sensor unit 800.

The touch panel 700 described in this embodiment includes the flexible input device 100 including the plurality of sensor units 800, each of which is provided with the windows 14 transmitting visible light, and the flexible display part 701 including the plurality of pixels 702 overlapping with the windows 14. The coloring layer is included between the window 14 and the pixel 702.

With such a structure, the touch panel can supply a sensor signal based on the change in the capacitance and positional data of the sensor unit supplying the sensor signal, can display image data associated with the positional data of the sensor unit, and can be bent. As a result, a novel touch panel with high convenience or high reliability can be provided.

The touch panel 700 may include an FPC 712 to which a signal from the input device 100 is supplied and/or an FPC 713 supplying a signal including image data to the display part 701.

In addition, a protective layer 17 p protecting the touch panel 700 by preventing damage and/or an anti-reflective layer 767 p that weakens the intensity of external light reflected by the touch panel 700 may be included.

Moreover, the touch panel 700 includes a scan line driver circuit 703 g which supplies the selection signal to a scan line of the display part 701, a wiring 711 supplying a signal, and a terminal 719 electrically connected to the FPC 713.

Components of the touch panel 700 are described below. Note that these components cannot be clearly distinguished and one component also serves as another component or includes part of another component in some cases.

For example, the input device 100 including the coloring layer overlapping with the plurality of windows 14 also serves as a color filter.

Furthermore, for example, the touch panel 700 in which the input device 100 overlaps the display part 701 serves as the input device 100 as well as the display part 701.

The touch panel 700 includes the input device 100 and the display part 701 (FIG. 32A). The input device 100 includes the plurality of sensor units 800 and the flexible base material 16 supporting the sensor units. For example, the plurality of sensor units 800 are arranged in matrix with 40 rows and 15 columns on the flexible base material 16.

The window 14 transmits visible light.

For example, the window 14 may be formed as follows: the base material 16, the sensor element C, and a flexible protective base material 17 each formed using a material transmitting visible light or a material thin enough to transmit visible light overlap with each other such that transmission of visible light is not prevented.

For example, an opening may be provided in a material that does not transmit visible light. Specifically, one opening or a plurality of openings having any of a variety of shapes such as a rectangle may be provided.

A coloring layer that transmits light of a predetermined color is provided to overlap with the window 14. For example, a coloring layer CFB transmitting blue light, a coloring layer CFG transmitting green light, and a coloring layer CFR transmitting red light are included (FIG. 32A).

Note that in addition to the coloring layers transmitting blue light, green light, and/or red light, coloring layers transmitting light of various colors such as a coloring layer transmitting white light and a coloring layer transmitting yellow light can be included.

For a coloring layer, a metal material, a resin material, a pigment, dye, or the like can be used.

A light-blocking layer BM is provided to surround the windows 14. The light-blocking layer BM does not easily transmit light as compared to the window 14.

For the light-blocking layer BM, carbon black, a metal oxide, a composite oxide containing a solid solution of a plurality of metal oxides, or the like can be used.

The scan line G1, the signal line DL, a wiring VPI, a wiring RES, a wiring VRES, and the sensing circuit 19 are provided to overlap with the light-blocking layer BM.

Note that a light-transmitting overcoat covering the coloring layer and the light-blocking layer BM can be provided.

As the flexible base material 16 and the flexible base material 710, an organic material, an inorganic material, or a composite material of an organic material and an inorganic material can be used.

For the base material 16 and the base material 710, a material with a thickness of 5 μm or more and 2500 μm or less, preferably 5 μm or more and 680 μm or less, further preferably 5 μm or more and 170 μm or less, still further preferably 5 μm or more and 45 μm or less, yet still further preferably 8 μm or more and 25 μm or less can be used.

A material with which passage of impurities is inhibited can be favorably used for the base material 16 and the base material 710. For example, a material with a vapor permeability of lower than or equal to 10⁻⁵ g/(m²·day), preferably lower than or equal to 10⁻⁶ g/(m²·day) can be favorably used.

The base material 710 can be favorably formed using a material whose coefficient of linear expansion is substantially equal to that of the material of the base material 16. For example, the base material 710 and the base material 16 can each be formed using a material whose coefficient of linear expansion is preferably lower than or equal to 1×10⁻³/K, further preferably lower than or equal to 5×10⁻⁵/K, and still further preferably lower than or equal to 1×10⁻⁵/K.

Examples of the materials of the base material 16 and the base material 710 are organic materials such as a resin, a resin film, and a plastic film.

Examples of the materials of the base material 16 and the base material 710 are inorganic materials such as a metal plate and a thin glass plate with a thickness of more than or equal to 10 μm and less than or equal to 50 μm.

The input device 100 can include the flexible protective base material 17 and/or the protective layer 17 p. The flexible protective base material 17 or the protective layer 17 p protects the input device 100 by preventing damage.

The display part 701 includes a plurality of pixels 702 arranged in matrix (FIG. 32B). For example, the pixel 702 includes a sub-pixel 702B, a sub-pixel 702G, and a sub-pixel 702R, and each sub-pixel includes a display element and a pixel circuit for driving the display element.

Note that in the pixel 702, the sub-pixel 702B is located to overlap with the coloring layer CFB, the sub-pixel 702G is located to overlap with the coloring layer CFG, and the sub-pixel 702R is located to overlap with the coloring layer CFR.

The display part 701 may include the anti-reflective layer 767 p positioned in a region overlapping with pixels. As the anti-reflective layer 767 p, a circular polarizing plate can be used, for example.

The display part 701 includes the wiring 711 through which a signal can be supplied. The wiring 711 is provided with the terminal 719. Note that the FPC 713 through which a signal such as an image signal or a synchronization signal can be supplied is electrically connected to the terminal 719.

Note that a printed wiring board (PWB) may be attached to the FPC 713.

«Sensor Element C»

The sensor element C is described giving an example that uses a capacitor. The capacitor includes a pair of electrodes. The capacitor includes an insulating film as the dielectric layer between the pair of electrodes.

When an object whose dielectric constant is different from that of the air gets closer to one of the pair of electrodes of the sensor element C that is put in the air, the capacitance of the sensor element C is changed. Specifically, when a finger or the like gets closer to the sensor element C, the capacitance of the sensor element C is changed. Thus, the sensor element C can be used in a proximity sensor.

When the sensor element C is changed in shape, the capacitance is changed with the change in shape.

Specifically, when a finger or the like is in contact with the sensor element C, and the gap between the pair of electrodes becomes small, the capacitance of the sensor element C is increased. Accordingly, the sensor element C can be used in a tactile sensor.

Specifically, when the sensor element C is bent, and the gap between the pair of electrodes becomes small, the capacitance of the sensor element C is increased. Accordingly, the sensor element C can also be used in a bend sensor.

«Sensing Circuit 19 and Converter CONV»

FIGS. 33A, 33B1, 33B2, and 33C illustrate configurations of the sensing circuit 19 and a converter CONV and a driving method of the sensing circuit 19 that are embodiments of the present invention.

FIG. 33A is a circuit diagram illustrating configurations of the sensing circuit 19 and the converter CONY of embodiments of the present invention, and FIGS. 33B1 and 33B2 are timing charts illustrating a driving method of one embodiment of the present invention. FIG. 33C shows the converter CONV that is different from the converter CONV shown in FIG. 33A. FIG. 34A shows the sensor circuits 19 in matrix.

The sensing circuit 19 includes transistors M1 to M3, for example (FIG. 33A and FIG. 34A). In addition, the sensing circuit 19 includes wirings that supply a power supply potential and a signal. For example, the signal line DL, the wiring VPI, a wiring CS, the scan line G1, the wiring RES, the wiring VRES, and the like are included.

Note that the sensing circuit 19 may be located not to overlap with the window 14.

Furthermore, the transistors M1 to M3 each include a semiconductor layer. For example, for the semiconductor layer, an element belonging to Group 14, a compound semiconductor, or an oxide semiconductor can be used. Specifically, a semiconductor containing silicon, a semiconductor containing gallium arsenide, an oxide semiconductor containing indium, or the like can be used.

Transistors that can be formed in the same process can be used as the transistors M1 to M3.

Any one of the transistors M1 to M3 preferably includes an oxide semiconductor layer. At this time, the oxide semiconductor layer and the oxide conductor layer are preferably located over the same surface. The off-state current of a transistor including an oxide semiconductor layer is small; therefore, it is particularly preferable that the transistor M1 include the oxide semiconductor layer.

For the wiring, a conductive material can be used. For example, an inorganic conductive material, an organic conductive material, a metal material, a conductive ceramic material, or the like can be used for the wiring. Specifically, a material that is the same as those of the pair of electrodes of the capacitor can be used.

For the scan line G1, the signal line DL, the wiring VPI, the wiring RES, and the wiring VRES, a metal material such as aluminum, gold, platinum, silver, nickel, titanium, tungsten, chromium, molybdenum, iron, cobalt, copper, or palladium, or an alloy material containing any of these metal materials can be used.

The sensing circuit 19 may be formed over the base material 16 by processing a film formed over the base material 16.

Alternatively, the sensing circuit 19 formed over another base material may be transferred to the base material 16.

Various circuits that can convert the sensor signal DATA supplied from the sensor unit 800 and supply the converted signal to the FPC1 can be used as the converter CONV (FIG. 32A). For example, a transistor M4 can be used in the converter CONV. Furthermore, as shown in FIG. 33C, the transistor M4 and a transistor M5 can be used in the converter CONV.

The sensing circuit 19 of one embodiment of the present invention includes the transistor M1 whose gate is electrically connected to one electrode of the sensor element C and whose first electrode is electrically connected to the wiring VPI that can supply a ground potential, for example (see FIG. 33A).

The sensing circuit 19 may further include the transistor M2 whose gate is electrically connected to the scan line G1 that can supply a selection signal, whose first electrode is electrically connected to a second electrode of the transistor M1, and whose second electrode is electrically connected to the signal line DL that can supply the sensor signal DATA, for example.

The sensing circuit 19 may further include the transistor M3 whose gate is electrically connected to the wiring RES that can supply a reset signal, whose first electrode is electrically connected to the one electrode of the sensor element C, and whose second electrode is electrically connected to the wiring VRES that can supply, for example, a ground potential.

The capacitance of the sensor element C is changed when an object gets close to the pair of electrodes or when the distance between the pair of electrodes is changed. Thus, the sensing circuit 19 can supply the sensor signal DATA based on a change in the capacitance of the sensor element C.

The sensing circuit 19 is provided with the wiring CS that can supply a control signal for controlling the potential of the other electrode of the sensor element C.

Note that a node at which the one electrode of the sensor element C, the gate of the transistor M1, and the first electrode of the transistor M3 are electrically connected to one another is referred to as a node A.

The wiring VRES and wiring VPI each can supply a ground potential, for example, and a wiring VPO and a wiring BR each can supply a high power supply potential, for example. Furthermore, the wiring RES can supply the reset signal, and the scan line G1 can supply the selection signal. Furthermore, the signal line DL can supply the sensor signal DATA, and a terminal OUT can supply a signal converted based on the sensor signal DATA.

Any of various circuits that can convert the sensor signal DATA and supply the converted signal to the terminal OUT can be used as the converter CONV. For example, a source follower circuit, a current mirror circuit, or the like may be formed by the electrical connection between the converter CONV and the sensing circuit 19.

Specifically, by using the converter CONV including the transistor M4, a source follower circuit can be formed (FIG. 33A). Furthermore, as shown in FIG. 33C, the converter CONV may include the transistors M4 and M5. Note that transistors that can be formed in the same process as those of the transistor M1 to the transistor M3 may be used as the transistors M4 and M5.

As described above, in the active matrix touch sensor of one embodiment of the present invention, the electrode of the sensor element and the read wiring can be formed in different layers. As shown in FIG. 34B, one electrode CM of a capacitor and a wiring ML are formed in different layers, and the width of the wiring ML is made narrow. Thus, the parasitic capacitance can be small and the adverse effect of noise can be suppressed. Accordingly, a decrease in the detection sensitivity of the touch sensor can be suppressed. Note that the one electrode CM of the capacitor overlaps with the plurality of pixels 702 shown in FIG. 34C that is an enlarged view of FIG. 34B.

<Driving Method of Sensing Circuit 19>

A driving method of the sensing circuit 19 is described.

«First Step»

In a first step, after the transistor M3 is turned on, a reset signal for turning off the transistor M3 is supplied to the gate of the transistor M3, so that the potential of the first electrode of the sensor element C is set to a predetermined potential (see Period T1 in FIG. 33B1).

Specifically, the reset signal is supplied from the wiring RES. The transistor M3 supplied with the reset signal renders the potential of the node A a ground potential, for example (see FIG. 33A).

«Second Step»

In a second step, a selection signal that turns on the transistor M2 is supplied to the gate of the transistor M2, and the second electrode of the transistor M1 is electrically connected to the signal line DL.

Specifically, the selection signal is supplied from the scan line G1. Through the transistor M2 to which the selection signal is supplied, the second electrode of the transistor M1 is electrically connected to the signal line DL (see a period T2 in FIG. 33B1).

«Third Step»

In a third step, a control signal is supplied to the second electrode of the sensor element, and a potential changed in accordance with the control signal and the capacitance of the sensor element C is supplied to the gate of the transistor M1.

Specifically, a rectangular control signal is supplied from the wiring CS. The sensor element C whose second electrode is supplied with the rectangular control signal increases the potential of the node A in accordance with the capacitance of the sensor element C (see the latter part of Period T2 in FIG. 33B1).

For example, in the case where the sensor element C is put in the air, when an object whose dielectric constant is higher than that of the air is placed closer to the second electrode of the sensor element C, the capacitance of the sensor element C is apparently increased.

Thus, the change in the potential of the node A caused by the rectangular control signal becomes smaller than that in the case where an object whose dielectric constant is higher than that of the air is not placed close to the second electrode of the sensor element C (see a solid line in FIG. 33B2).

«Fourth Step»

In a fourth step, a signal obtained by the change in the potential of the gate of the transistor M1 is supplied to the signal line DL.

For example, a change in current due to the change in the potential of the gate of the transistor M1 is supplied to the signal line DL.

The converter CONV converts the change in the current flowing through the signal line DL into a change in voltage and supplies the voltage.

«Fifth Step»

In a fifth step, a selection signal for turning off the transistor M2 is supplied to the gate of the transistor M2.

FIG. 35 is a cross-sectional view illustrating the structure of the above-described touch panel. FIG. 35 illustrates an example in which the display device in FIGS. 7A and 7B is provided with a touch sensor. In the touch panel, the transistor of the sensing circuit 19 and a capacitor 340 are formed on the second substrate 42 side.

One electrode 341 of the capacitor 340 is formed to overlap with the coloring layer 336, using a material transmitting the light passing through the coloring layer 336. The other electrode 342 of the capacitor 340 can be formed using, for example, the same material as a semiconductor layer of the transistor. For example, an oxide conductor layer formed by adding impurities forming oxygen vacancies, impurities forming donor levels, or the like to an oxide semiconductor layer can be used.

The structure described in this embodiment can be used in appropriate combination with the structure described in any of the other embodiments.

Embodiment 7

In this embodiment, electronic devices to which one embodiment of the present invention is applied will be described with reference to FIGS. 36A and 36B.

Highly reliable flexible electronic devices can be manufactured by adopting the display device of one embodiment of the present invention.

Examples of the electronic devices to which the display device of one embodiment of the present invention is applicable are a television device, a monitor of a computer or the like, digital signage, a digital photo frame, a mobile phone, a portable game console, a portable information terminal, an audio reproducing device, and the like.

FIG. 36A illustrates an example of a thin portable information terminal. A portable information terminal 7100 includes a display part 7102 incorporated in a housing 7101, a speaker 7103, a microphone 7106, a camera 7107, and the like. Note that the housing 7101, the display part 7102, and the like are flexible as shown in FIG. 36B, which leads to excellent portability and high resistance against shock such as a drop impact. The display part 7102 includes the display device of one embodiment of the present invention, and for example, an image displayed on the display part can be changed by the action of bending or the like. Therefore, the display part 7102 is particularly suitable for an electronic book or the like.

The structure described in this embodiment can be used in appropriate combination with the structure described in any of the other embodiments.

This application is based on Japanese Patent Application serial no. 2014-095200 filed with Japan Patent Office on May 2, 2014, the entire contents of which are hereby incorporated by reference. 

What is claimed is:
 1. A method for operating a display device, comprising the steps of: displaying a first image on a display part; first determining whether a curvature of an edge or a vicinity of a center region of the display part is larger than or equal to a first set value, wherein, when the curvature is smaller than the first set value, the step of first determining of the curvature is performed again; displaying an image for operation on the edge of the display part when the curvature is larger than or equal to the first set value; first detecting, on the image for operation, a position of an object touching the image; second detecting, on the image for operation, a change in the position of the object; second determining whether a curvature of the edge of the display part is larger than or equal to a second set value when the change in the position of the object is not detected in the step of second detecting, wherein when the curvature is smaller than the second set value, the step of second detecting is performed again; and changing the first image to a second image when the change in the position of the object is detected in the step of second detecting, wherein, when the curvature is larger than or equal to the second set value in the step of second determining, the step of changing is performed.
 2. The method for operating a display device, according to claim 2, wherein the steps from displaying to changing are performed sequentially and repeatedly while the second image displayed on the display part in the step of changing is used as the first image displayed on the display part in the step of displaying. 